System and method for generation of point of use reactive oxygen species

ABSTRACT

Systems and methods for generating reactive oxygen species formulations useful in various oxidation applications. Exemplary formulations include singlet oxygen or superoxide and can also contain hydroxyl radicals or hydroperoxy radicals, among others. Formulations can contain other reactive species, including other radicals. Exemplary formulations containing peracids are activated to generate singlet oxygen. Exemplary formulations include those containing a mixture of superoxide and hydrogen peroxide. Exemplary formulations include those in which one or more components of the formulation are generated electrochemically. Formulations of the invention containing reactive oxygen species can be further activated to generate reactive oxygen species using activation chosen from a Fenton or Fenton-like catalyst, ultrasound, ultraviolet radiation or thermal activation. Exemplary applications of the formulations of the invention among others include: cleaning in place applications, water treatment, soil decontamination and flushing of well casings and water distribution pipes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application61/698,550 filed Sep. 7, 2012, which is incorporated by reference hereinin its entirety.

BACKGROUND

It is well known that a combination of reactive oxidant species can bebeneficial to water treatment, cleaning, decontamination and remediationapplications as they will combat a variety of substrate types which maybe present and react with a variety of oxidation byproducts during theirbreakdown.

Hydroxyl Radicals

Of the common oxidants used in water treatment and remediation, thehydroxyl radical has the most positive standard oxidation potential of2.80 V and is very effective at oxidizing a wide variety of substances.Hydroxyl radicals react very rapidly with a wide variety of oxidizablesubstrates. However, the hydroxyl radical lifetime is very short inaqueous media, merely several nanoseconds, and therefore must beproduced with several tens of angstroms of a target substrate due tominimal diffusion path length. Hydroxyl radicals can further be quenchedby undesirable reactions including reactions with radical quenchers,precursor oxidants and other hydroxyl radicals. For example, carbonateand bicarbonate ions present in natural waters are effective radicalquenchers. Further, hydrogen peroxide and ozone can react with hydroxylradicals; therefore while generating hydroxyl radicals from hydrogenperoxide and/or ozone precursors in water, the precursor istraditionally kept below 10 g/mL to avoid excessive consumption ofhydroxyl radicals by the parent oxidant.

One issue with using hydroxyl radicals in water treatment is theirability to oxidize halide salts with much lower standard potentials andeven oxidize sulfate diaion to the persulfate radical anion. A singleelectron oxidation of halide by a hydroxyl radical will producehypochlorous acid, hypobromous acid and their hypohalite forms dependingon the pH. However, an excess of hydroxyl radicals in the presence ofhypohalites will further oxidize them in subsequent steps to chlorate,which is toxic, and bromate, which is carcinogenic.

Fenton Catalyst Activation

Fenton catalyst activation of hydrogen peroxide occurs when a reducediron species, Fe²⁺, is oxidized by hydrogen peroxide thereby producinghydoxyl radical, .OH, and an oxidized iron species, Fe³⁺. The catalyticcycle is completed when hydrogen peroxide reduces Fe³⁺ back to Fe²⁺thereby producing hydroperoxyl radical HOO., which is in equilibriumwith superoxide. The Fenton process is summarized in Equations A and B,below.

Fe²⁺+H₂O₂→Fe³⁺+.OH+OH⁻  Eq. A:

Fe³⁺+H₂O₂→Fe²⁺+.OOH+H⁺  Eq. B:

Similar Fenton-like chemistry occurs with other peroxides such asperoxyacetic acid. Iron sulfate is the most common Fenton catalyst andmust be used at a pH near or below pH 4 to avoid excessive precipitationof Fe³⁺ oxides and oxyhydroxides. Other iron catalyst forms such as ironminerals (e.g., magnetite) and chelated iron compounds have stability athigher pH.

Ultrasound Activation

Ultrasound activation of hydrogen peroxide in aqueous solution occurswhen ultrasound waves induce cavitation of water forming bubbles, whichleads to very high localized heating as cavitation bubbles collapseresulting in the thermal dissociation of hydrogen peroxide to hydroxylradicals in Equation C.

H₂O₂+heat→2.OH  Eq. C:

Similar thermal dissociation of peracids occurs to generate twodifferent radical species in Equation D.

AcOOH+heat→AcO.+.OH  Eq. D:

Ultraviolet Activation

Ultraviolet light activation of hydrogen peroxide occurs by theabsorption of ultraviolet light, typically in the wavelength range of180 to 220 nanometers, which leads to dissociation of hydrogen peroxideforming hydroxyl radicals summarized in Equation E.

H₂O₂+UV light→2.OH  Eq E:

Similar ultraviolet activation and dissociation of peracids occurs togenerate two different radical species in Equation F.

AcOOH+UV light→AcO.+.OH  Eq. F:

Thermal Activation:

Thermal activation of hydrogen peroxide can be conducted by impinging aliquid, spray, mist, vapor, or steam containing hydrogen peroxide upon ahot surface coated with a catalyst (e.g., silver oxide, iron oxide,ruthenium oxide, glass, quartz, Mo glass, Fe_(3-x)Mn_(x)O₄ spinels,Fe₂O₃ with Cu-ferrite, MgO and Al₂O₃.) and heated to above 200° C., toform hydroxyl radicals in Equation G.

H₂O₂+heat+catalyst surface→2.OH  Eq. G:

The initial peroxide activation step in Equation G is followed by aseries of radical propagation steps in the gas phase where intermediateradical species form such as the hydroperoxyl radical.

Singlet oxygen is a molecular oxygen in an excited electronic state.Singlet oxygen is most commonly produce in aqueous solutions byphotolysis of dissolved oxygen directly by ultraviolet radiation orindirectly by energy transfer from a visible light photosensitizer dyeto molecular oxygen. The use of photosensitizing dyes such as methyleneblue, certain metalloporphyrins, semiconductors and other materials togenerate singlet oxygen to degrade contaminants in water, disinfectionand other uses are not practical for wastewater treatment due todegradation of dyes by singlet oxygen over time (i.e., photobleaching)and at elevated concentrations.

Another common method of singlet oxygen generation is by chemicalreactions where singlet oxygen is released as a byproduct, including theHaber-Weiss reaction, reaction between hydrogen peroxide andhypochlorite, decomposition of 9,10-diphenylanthracene endoperoxide anda reaction between neutral and ionized forms of organic peroxyacids.However, these methods cause the rapid quenching of the singlet oxygenspecies by physical and chemical pathways. Chemical quenching reactionsoccur when singlet oxygen is consumed by a non-beneficial chemicalreaction involving electron transfer. Physical quenching reactions occurby radiative or non-radiative relaxation of the excited state byphysical contact with its surroundings without electron transfer. Inthese methods, excess hydrogen peroxide is a very effective quenchingagent resulting in little or no oxidative activity from singlet oxygengenerated in the presence of significant concentrations of hydrogenperoxide. When hydrogen peroxide is present in significantconcentrations, as is the case for most commercially producedperoxyacetic acid, singlet oxygen is rapidly quenched by hydrogenperoxide, which reduces singlet oxygen concentration. Chlorine, azide,certain tertiary amines and beta-carotene are other known examples ofsinglet oxygen quenchers.

Peroxyacetic acid (i.e. AcOOH) is typically made by commercial producersby an equilibrium reaction between concentrated acetic acid (i.e. AcOH).The equilibrium reaction can be catalyzed by a mineral acid such assulfuric acid at a pH<1 and occurs over a time period of several hoursto several days depending on the concentration of hydrogen peroxide,acetic acid and acid catalyst. There is typically a significantconcentration of residual hydrogen peroxide and acetic acid inperoxyacetic acid made by the equilibrium reaction. For example, the[peroxyacetic acid][H₂O]/[acetic acid][H₂O₂] concentration ratios areoften between 1.8 and 2.5 for commercial grades between 5 and 30 wt %peroxyacetic acid. Peroxyacetic acid solutions are generally unstable atroom temperature and pose a significant fire hazard. Thereforeperoxyacetic acid is typically produced on site by the equilibriumprocess or shipped in vented containers from a producer. Peroxyaceticacid may be distilled under reduced pressure to obtain a pure form withlow hydrogen peroxide residual, however, distillation is generally notpractical and can create a severe explosion hazard.

Superoxide is the radical anion form of molecular oxygen and is a mildreducing agent with a standard oxidation potential commonly reported as−0.33 V in aqueous environments. Superoxide can be produced in bulk asthe anhydrous potassium salt, KO₂, which rapidly reacts with water orcarbon dioxide releasing molecular oxygen and potassium hydroxide orpotassium carbonate, respectively. Superoxide can also be produced insitu by ultraviolet irradiation of oxygen containing solutions includingseawater, enzymatic processes and by electrochemical reduction ofoxygen. For large scale applications superoxide is typically supplied asa bulk chemical or generated in situ from activated hydrogen peroxidereactions. Potassium superoxide is a water-sensitive hazardous materialand combustion aid, which may be prohibitive barriers to its use in somelocations. Also, potassium superoxide must be fed into a treatmentprocess as a solid feed, which can be problematic due to waterabsorption, caking and clogging of solid feeders.

Several common issues arise with conventional reactive oxygen speciesformulations including, for example, limited shelf life, low mobility ofoxidants and/or catalysts; highly acidic or alkaline oxidants whichcause significant changes in the natural soil or groundwater pH; limitedoptions for oxidant types available from a single product or system; andlogistic, cost, permitting or safety issues associated with bringinglarge quantities of strong oxidizers and hazardous chemicals on site.Additionally, the use of conventional iron-based hydrogen peroxideFenton catalysts and sodium persulfate activators, such as iron (II)sulfate, require an acidic pH of less than 4 to be active, but as the pHincreases toward neutral pH levels the precipitation of iron oxides andoxyhydroxides occurs. Precipitated iron can cause pore plugging insoils, fouling and staining equipment and can promote population bloomsof iron bacteria which cause biofouling of soils, and acceleratedmicrobial corrosion of steel well casings, pipes and equipment.

Well Flushing:

Oil and gas production wells, groundwater wells and water pipelines areoften hyper-chlorinated to control microbial growth and slime buildupwith varying degrees of success due to issues such as organic residues,slime buildup and incompatible pH. Chlorine and hypochlorite are readilysequestered by organics residues and slime materials, which protectactive microbes from being killed. Hypochlorite also rapidly loses itsefficacy above pH 7.5, below the natural pH of seawater and many groundwater types with pH levels greater than 8.

SUMMARY OF THE INVENTION

The invention provides reactive oxygen species formulations as well asmethods for making and using such formulations.

In an embodiment, the invention provides a method for generating areactive oxygen species formulation comprising (1) generating analkaline hydrogen peroxide solution from the combination of an alkaliand a hydrogen peroxide concentrate; (2) mixing the alkaline hydrogenperoxide solution with an acyl or acetyl donor such that a peracidconcentrate is produced, wherein the peracid concentrate has minimalhydrogen peroxide residual; and (3) adjusting the peracid pH level tothe activated pH range for generating the reactive oxygen species. Thereactive oxygen species formulation can be a singlet oxygen precursorformulation. In an embodiment, the hydrogen peroxide solution isgenerated using a molar ratio of H₂O₂ to alkali in the range of 1:1.2 to1:2.5. The molar ratio of H₂O₂ to alkali can be 1:1.2 to 1:1.4, 1.4 to1:2.0 or 1:2.0 to 1:2.5. In an embodiment, the peracid concentrate isproduced by mixing the alkaline hydrogen peroxide solution with the acylor acetyl donor such that the molar ratio of hydrogen peroxide to acylor acetyl donor ranges from 1:1.25 to 1:4. The molar ratio of hydrogenperoxide to acyl or acetyl donor can be 1:1.25 to 1:1.5, 1:1.5 to 1:2,or 1:2 to 1:4. In an embodiment, the activated pH range is in the rangeof pH 6.5 to 12.5. The activated pH range can be 6.5 to 9.5 or 9.5 to12.5. In an embodiment, the method further comprises entrainingbyproducts of the reaction between the alkaline hydrogen peroxidesolution and the acyl or acetyl donor. In an embodiment, the methodfurther comprises diluting the peracid concentrate. In an embodiment,the method further comprises mixing the peracid solution with anadditives concentrate. In an embodiment, the method comprises storingthe alkaline hydrogen peroxide in a holding tank for immediate or futureuse. In an embodiment, mixing the alkaline hydrogen peroxide solutionwith an acyl or acetyl donor produces a concentrated peracid solution.

In an embodiment, the invention provides a method for generating areactive oxygen species formulation wherein an alkaline hydrogenperoxide concentrate is electrochemically generating, theelectrochemically generated alkaline hydrogen peroxide concentrate iscombined with an acyl or acetyl donor to produce a peracid concentrate,wherein the peracid concentrate has minimal hydrogen peroxide residualand the peracid solution is combined with an acid concentrate to producethe reactive oxygen species formulation having a pH level in theactivated pH range. In an embodiment, the electrochemically generatedalkaline hydrogen peroxide concentrate has a pH in the range of 12.0 to13.0, and a percent weight of hydrogen peroxide in the range of 0.1 to 3wt %. In an embodiment, the acid concentrate is co-generated duringelectrochemically generating the alkaline hydrogen peroxide concentrate.The co-generated acid concentrate can have 0.1 wt % to 20 wt % acid. Inan embodiment, the peracid concentrate is produced by mixing theelectrochemically generated alkaline hydrogen peroxide solution with theacyl or acetyl donor such that the molar ratio of hydrogen peroxide toacyl or acetyl donor is in the range of 1:1.25 to 1:4. The molar ratioof hydrogen peroxide to acyl or acetyl donor can be 1:1.25 to 1:1.5,1:1.5 to 1:2, or 1:2 to 1:4. In an embodiment, the activated pH range isin the range of pH 6.5 to 12.5. The activated pH range can be 6.5 to 9.5or 9.5 to 12.5. In an embodiment, the method further comprisesentraining byproducts of the reaction between the alkaline hydrogenperoxide solution and the acyl or acetyl donor. In an embodiment, themethod further comprises diluting the peracid concentrate. In anembodiment, the method further comprises mixing the peracid solutionwith an additives concentrate. In an embodiment, the method comprisesstoring the alkaline hydrogen peroxide in a holding tank for immediateor future use. In an embodiment, mixing the alkaline hydrogen peroxidesolution with an acyl or acetyl donor produces a concentrated peracidsolution.

In an embodiment, the invention provides a method for generating asuperoxide reactive oxygen species formulation comprisingelectrochemically co-generating a solution containing hydrogen peroxideand superoxide. In an embodiment, the formulation containingco-generated hydrogen peroxide and superoxide has a pH of 8-13. In anembodiment, the molar ratio of superoxide to hydrogen peroxideco-generated ranges from 0.01:1 to 10:1. In an embodiment, the pH of thesuperoxide solution is adjusted by addition of an acid concentrate. Inan embodiment, the acid concentrate is co-generated during the step ofelectrochemically generating the superoxide solution. In an embodiment,the superoxide solution is combined with an additives concentrate. In anembodiment, the superoxide solution is diluted. More specifically, thesuperoxide solution is diluted to a near point of use concentration. Inan embodiment, co-generation of hydrogen peroxide and superoxideproduces at least one radical species which can among others be ahydroperoxyl radical and/or a hydroxyl radical.

In related embodiments, the methods for generating reactive oxygenformulations further comprise further activating the reactive oxygenspecies using activation chosen from the group a Fenton or Fenton-likecatalyst, ultrasound, ultraviolet radiation and thermal activation. Morespecifically activation produces radical species, which can be thehydroxyl radical.

In an embodiment, a reactive oxygen formulation produced by the methodsherein is distributed to its point of use. The form in which thereactive oxygen formulation is distributed can as a liquid, an ice, afoam, an emulsion, a microemulsion or an aerosol. The invention alsoprovides reactive oxygen formulations for point of use applicationswhich are appropriately formulated for application by injection,flooding, spraying, and/or circulation.

In specific embodiments, in the methods herein the reactive oxygenspecies is singlet oxygen. The invention also provides formulationscontaining reactive oxygen species, particularly those prepared by themethods of the invention. In specific embodiments, the reactive oxygenspecies formulations are singlet oxygen formulations. Such formulationscan be concentrated or can be diluted. Diluted formulation can beprepared by addition of water.

In specific embodiments, the invention provides a reactive oxygenspecies precursor comprising a peracid concentrate comprising a mixtureof alkaline hydrogen peroxide and an acyl or acetyl donor. The reactiveoxygen species precursor can be a diluted singlet oxygen precursor. Morespecifically, the diluted singlet oxygen precursor has a pH in the range6.5 to 12.5, in the range 6.5 to 9.5 or in the range 9.5 to 12.5. Thereactive oxygen species precursor can be a concentrated singlet oxygenprecursor. More specifically, the concentrated singlet oxygen precursorhas a pH in the range 6.5 to 12.5, in the range 6.5 to 9.5 or in therange 9.5 to 12.5.

In an embodiment, the invention provides a peracid formulation capableof generating singlet oxygen, particularly where the singlet oxygen isgenerated by the reaction of alkaline hydrogen peroxide and an acyl oracetyl donor. The invention also provides a method for making suchperacid formulations. Preferably the peracid formulation has minimalhydrogen peroxide residual to minimize quenching of the singlet oxygen.In an embodiment, the peracid formulation has a pH in the activated pHrange. In a specific embodiment, in the peracid formulation, the ratioof alkaline hydrogen peroxide to acyl or acetyl donor reactive groups isin the range 1:1.25 to 1:2 to 1:4. More specifically, the ratio ofalkaline hydrogen peroxide to acyl or acetyl donor reactive groups is1:1.25 to 1:1.5, 1:1.5 to 1:2, or 1:2 to 1:4. The peracid formulationcan have pH in the range 6.5 to 12.5, 6.5 to 9.5 or 9.5 to 12.5. In aspecific embodiment, the peracid formulation is further reacted with anacid concentration resulting in both peracetic acid and paracetic acidanion, wherein the reaction of the peracid formulation and acidconcentrate comprises the reaction:

AcOOH+AcOO⁻→¹O₂+AcOH+AcO⁻.

Peracid formulation of the invention can be distributed in any suitableform and can be distributed in the form of a liquid, an ice, a foam, anemulsion, a microemulsion or an aerosol. The peracid formulations of theinvention can be applied to a point of use by an application chosen frominjection, flooding, spraying, and circulation. The peracid formulationsof the invention can be used for clean-in-place applications in food,dairy, beverage and biopharma; hard surface cleaning; decontamination;remediation of soil and groundwater; cleaning of membrane filtrationsystems; flushing of well casings and water distribution pipes; andin-situ chemical oxidation, among others.

In an embodiment, the invention provides an electrochemically generated,reactive oxygen species solution comprising superoxide formulationco-generated with a hydrogen peroxide solution. More specifically, thesuperoxide to hydrogen peroxide solutions are generated such that theratio of superoxide to hydrogen peroxide is 0.01:1 to 10:1. Morespecifically, the superoxide to hydrogen peroxide solutions aregenerated such that the ratio of superoxide to hydrogen peroxide rangesfrom 0.01:1 to 0.5:1, from 0.5:1 to 1.5:1, from 1.5:1 to 3:1, from 3:1to 5:1, or from 5:1 to 10:1. In an embodiment, the electrochemicallygenerated, reactive oxygen species solution has initial pH of 8-13, or8-9, or 9-12, or 12-13.

In an embodiment, the invention provides a formulation containing anelectrochemically generated hydroperoxyl radical. In an embodiment, theradical is created by the reaction of electrochemically generatedsuperoxide formulation co-generated with hydrogen peroxide formulationby the reaction:

O₂.⁻+H₂O₂

¹O₂+.OH+OH⁻.

In an embodiment, the invention provides a method for treating wastewater employing formulations of the invention containing reactive oxygenspecies. In a specific embodiment, the method includes electrochemicallyco-generating a cathode output solution comprising superoxide andhydrogen peroxide; mixing the cathode output solution into a waste watersource; and adjusting the pH of the mixture. In an embodiment, pH isadjusted after the step of mixing the cathode output solution into thewaste water source.

Other embodiments of the invention will become apparent on review of thefollowing drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one exemplary system 100 for generation of a dilutedreactive oxygen species 116 using bulk chemical feedstock constituents,in an embodiment.

FIG. 2 shows an exemplary method 200 for generating reactive oxygenspecies output 116 using system 100 of FIG. 1.

FIG. 3 shows one exemplary system 300 for generation of a concentratedreactive oxygen species output 314 using bulk chemical precursorconstituents, in one embodiment.

FIG. 4 shows an exemplary method 400 for generating reactive oxygenspecies output 314 using system 300 of FIG. 3.

FIG. 5 shows an exemplary system 500 for generating chemicals using anelectrochemical reactor 514 to produce a diluted reactive oxygen speciesoutput.

FIGS. 6A/6B depict an exemplary a cross-sectional view of the generalconfiguration and components of an exemplary electrochemical reactor 600for use in system 500 of FIG. 5, in one embodiment.

FIG. 7 depicts an embodiment of a reactor system 700 that has a reactorsystem fluid process flow, also known as a flow pathway, that enablesgas recirculation within reactor system 700.

FIG. 8 shows an exemplary method 800 for generating a diluted reactiveoxygen species output 522 using system 500 of FIG. 5.

FIG. 9 shows an exemplary system 900 for generating chemicals using anelectrochemical reactor 914 and mixing the reactor's 914 outputstogether and optionally with other materials to produce a concentratedreactive oxygen species output 922.

FIG. 10 shows an exemplary method 1000 for generating a concentratedreactive oxygen species output 922 using system 900 of FIG. 9.

FIG. 11 shows an exemplary system 1100 for generating chemicals using anelectrochemical reactor 1114 to produce a superoxide reactive oxygenspecies output.

FIG. 12 shows an exemplary method 1200 for generating a concentratedsuperoxide reactive oxygen species output 1122 using system 1100 of FIG.11, in one embodiment.

FIG. 13 shows exemplary results of the percent color removal of 50 mg/LMB solutions observed over time starting with different initialperoxyacetic acid concentrations.

FIG. 14A shows graph 1400 that shows the full spectra of samples dilutedto 100+/−4 mg/L hydrogen peroxide and adjusted to pH 12.00+/−0.04.

FIG. 14B shows the spectra of FIG. 14A with hydrogen peroxide absorbancesubtracted off.

FIGS. 15A/B show graphs 1500, 1550 that show the evolution of the UVabsorbance spectrum over five hours for the co-generated hydrogenperoxide and superoxide output produced at 8 amps in Example 11 dilutedto 100+/−4 mg/L hydrogen peroxide, adjusted to pH 12.00+/−0.04 andanalyzed over time.

FIGS. 16A/B show graphs 1600, 1650 that shows the evolution of the UVabsorbance spectrum over five hours for the co-generated hydrogenperoxide and superoxide output produced at 8 amps in Example 11 dilutedto 100+/−8 mg/L hydrogen peroxide, adjusted to pH 11.04+/−0.04 andanalyzed over time.

FIG. 17 shows an exemplary system and flow process for electrochemicallygenerating a OP cleanser, in one embodiment.

FIG. 18 shows one exemplary system used in example 17 to show anexemplar of producing a superoxide precursor formulation using anelectrochemical generator used in a water treatment application, in oneembodiment.

DETAILED DESCRIPTION OF THE INVENTION Reactive Oxygen Species from BulkChemicals

In the following embodiments, systems and methods are shown to generatereactive oxygen species in situ from a mixture of bulk chemicalfeedstocks in close proximity to various substrates defined asmaterials, compounds, atoms or ions (organic or inorganic) to beoxidized or microorganisms to be denatured or killed.

In the following embodiments, exemplary systems and methods are shown,for example, that describe alternatives to the use of hydroxyl radicaloxidation chemistry that are more compatible with saline or highlycontaminated waters and minimizes chlorate and bromate formation byhaving lower standard oxidation potentials than chloride, bromide ortheir hypohalite forms while possessing high chemical reactivity towarda variety of substrates.

In another embodiment, an exemplary system and method is shown forenabling the production of larger quantities and higher concentrationsof singlet oxygen from chemical precursor formulations not containingsinglet oxygen quenching agents.

In yet another embodiment, an exemplary method and system is shown forsinglet oxygen production to occur for extended periods of time whilethe amount and rate of singlet oxygen evolved can be controlled by themore readily measurable precursor formulation and concentration.

FIG. 1 shows one exemplary system 100 for generation of a dilutedreactive oxygen species 116 using bulk chemical feedstock constituents,in an embodiment. In an embodiment, diluted reactive oxygen speciesoutput 116 is used in applications where a fluid is conveyed to asurface or material including clean in place, hard surface cleaning,decontamination, remediation and in situ chemical oxidationapplications. System 100 includes hydrogen peroxide (H₂O₂) concentrate102, alkali concentrate 104, acyl or acetyl donor 106, makeup water 108,additives concentrate 110, acid concentrate 112, peracid holding tank114, reactive oxygen species output 116, pumps 118, and mixing chambers120. In one embodiment, reactive oxygen species output 116 is dilutedsinglet oxygen precursor solution.

Hydrogen Peroxide Concentrate 102 is typically an aqueous hydrogenperoxide solution, for example. However, in alternative embodiments,hydrogen peroxide concentrate 102 may include other chemical forms ofperoxide chosen from the group including: calcium peroxide, potassiumperoxide, sodium peroxide, lithium peroxide, percarbonates, andperborates.

In one embodiment, alkali concentrate 104 is an aqueous sodium hydroxidesolution. In an alternative embodiment, Alkali concentrate 104 ispotassium hydroxide. Acyl or acetyl donor 106 or mixture of donors maybe in liquid or solid form, or dissolved in a solvent when reacted witha solution of hydrogen peroxide.

Acid concentrate 112, for example, includes at least one pH bufferchosen from the group including: weak acid electrolytes includingacetate, citrate, propionate, phosphate and sulfate.

In an embodiment, reactive oxygen species output 116 is a peroxyaceticacid in the absence of hydrogen peroxide and includes at least onechemical precursor species capable of releasing singlet oxygen. Inalternative embodiments, reactive oxygen species output 116 includes twochemical precursor species may be used to release singlet oxygen. In yetanother embodiment, reactive oxygen species output 116 includes morethan two chemical precursor species to release singlet oxygen.

FIG. 2 shows an exemplary method 200 for generating reactive oxygenspecies output 116 using system 100 of FIG. 1. In an embodiment, thereactive oxygen species output 116 generated by method 200 is singletoxygen. In step 202, an alkaline hydrogen peroxide anion solution 122 iscreated by mixing .H2O₂ concentrate 102 with alkali concentrate 104 inmixing tank 120(1). For example, molar ratios of .H2O₂ concentrate 102to alkali in alkali concentrate 104 may range from 1:1.2 to 1:2.5. In anembodiment, the preferred molar ratio range is 1:1.4 to 1:2, forexample. The preferred molar ratio range is determined by the preferredpH range of the alkaline hydrogen peroxide solution of pH 12.0 to 12.6,which promotes the reaction between hydrogen peroxide and the acyl oracetyl donor. In one embodiment, hydrogen peroxide concentrate 102 is aweak acid with a pKa of 11.6 and therefore its combination with alkaliconverts it in an acid-base equilibrium to the hydrogen peroxide anionform as in Equation 1 below:

HOOH+OH⁻

HOO⁻+H₂O  [1]

In some embodiments, raising the pH of a hydrogen peroxide solutionenough to put a significant proportion of hydrogen peroxide into theanion form requires an excess of alkali 104 over hydrogen peroxide 102.In one embodiment, the molar excess of alkali 104 over H₂O₂ 102 mayrange from 20% to 100% greater alkali 104. For example, a preferredmolar excess range is 20% to 40% greater alkali 104. The equilibriumreaction in Equation 1 consumes alkali in a 1:1 molar ratio, thereforean excess of alkali over hydrogen peroxide is required to raise the pHof the alkaline hydrogen peroxide solution to the preferred pH range.

In step 204, the resulting alkaline hydrogen peroxide 122 is combinedwith an acyl or acetyl donor 106 in mixing tank 120(2) to create aresulting alkaline peracid concentrate 122′. In one embodiment, alkalineperacid concentrate 122′ may be a peroxyacetic acid solution. In oneembodiment, the acyl or acetyl donor is added in proportion to thehydrogen peroxide. In an alternative embodiment, the molar ratio of H₂O₂122 to acyl or acetyl donor 106 reactive group equivalents can rangefrom 1:1.25 to 1:4. For example, a preferred molar ratio range is 1:1.5to 1:2. If the ratio is too low a high hydrogen peroxide residual willremain in the peracid concentrate where it will significantly quenchsinglet oxygen. If the ratio is higher than needed to achieve a lowhydrogen peroxide residual that does not significantly quench singletoxygen then excess acyl or acetyl donor is remains unused. In oneembodiment, the acyl or acetyl donor is an oxygen-acyl or oxygen-acetyldonor shown in Equation 2a below:

HOO⁻⁺AcOR→AcOO⁻⁺ROH  [2a]

Where Ac is acyl [—C(O)R′] or acetyl [—C(O)CH₃] and R and R′ arehydrocarbon-based substituents. In an alternative embodiment, the acylor acetyl donor is a nitrogen-acyl or nitrogen-acetyl donor as shown inEquation 2b below:

HOO⁻⁺AcNR₂→AcOO⁻⁺RNH  [2b]

Where Ac is acyl [—C(O)R′] or acetyl [—C(O)CH₃] and R and R′ arehydrocarbon-based substituents.

In Equations 2a/2b above, the reaction between an acyl or acetyl donor106 and hydrogen peroxide 122 occurs at alkaline pH by nucleophilicattack of the acyl carbonyl carbon atom by the hydrogen peroxide anion,which displaces the donor molecule fragment as an alcohol or amine in amanner analogous to saponification. In some embodiments, thenon-equilibrium reactions generalized in Equations 2a/2b are conductedbetween pH 10 and pH 13.

The use of non-equilibrium reaction in Equations 2a/2b produces alkalineperacid concentrate 122′ with concentrations of less than approximately5 wt % peroxyacetic acid and other organic peracids that are producedefficiently and rapidly. Using the non-equilibrium reaction allows thehydrogen peroxide residual to be minimized if necessary. Minimizing thehydrogen peroxide residual, for example, significantly increases theconcentration of the singlet oxygen available to oxidize targetsubstrates. In one embodiment, for example, the [peroxyaceticacid][water]/[hydrogen peroxide] concentration ratios are from 10, 100,or 1000 depending on the ratio of hydrogen peroxide to acyl or acetyldonor ratio in Equations 2a/2b.

In one embodiment, at least one molar equivalent of acyl or acetyl donor106 reactive groups is added for each equivalent of hydrogen peroxide inalkaline hydrogen peroxide anion solution 122 used in Equations 2a/2b toconsume all of the hydrogen peroxide. In alternative embodiments, excessacyl or acetyl donor 106 reactive groups is necessary to minimize thehydrogen peroxide residual due to the competing conversion of acyl oracetyl donor 106 reactive groups to the corresponding carboxylic acid bythe alkali concentrate 104 used to raise the pH of the H₂O₂ concentrate102. In one embodiment, the molar excess of acyl or acetyl donor 106reactive groups over H₂O₂ solution 122 may range from 25% to 300%greater acyl or acetyl donor 106. For example, a preferred molar excessrange is 50% to 100% greater acyl or acetyl donor 106 reactive groups.

In optional step 206, as indicated by the dashed lines, method 200entrains byproducts 124 produced by the reactions of Equations 2a/2b.For example, byproducts 124 are entrained in solution with the alkalineperacid concentrate 204. In one embodiment, byproducts 124 are useful asco-solvents, pH buffers, chelating agents or stabilizers and carbonsubstrates for microbial processes after a chemical oxidation process.For example, the byproduct 124 of acetyl donors 106 of monacetin,diacetin and triacetin is glycerol, a potential co-solvent and favorablecarbon source for microbes. In another embodiment, byproduct 124 ofacetyl donor 106 of TAED, diacetylethylenediamine, acts as a chelatingagent for transition metal ions and potentially serves as a peroxidestabilizer. In yet another embodiment, byproduct 124 is the carboxylicacid produced after alkaline peracid concentrate 122′ reacts with amaterial or decomposes. Alternatively, acetic acid, a byproduct 124 ofperoxyacetic acid, serves as a co-solvent, a pH buffer, a chelatingagent, and a biological substrate.

In step 208, method 200 dilutes the resulting alkaline peracidconcentrate 122′ to nearly point of use concentration by adding makeupwater 108. The amount of dilution is dependent on the concentration ofalkaline peracid concentrate 122′ and the desired point of useconcentration of reactive oxygen species output 116. For example thealkaline peracid concentration 122′ may be 19 wt % to 21 wt % using 50wt % hydrogen peroxide concentrate 102, 50 wt % sodium hydroxide as thealkali concentrate 104 and triacetin as the acetyl donor 106. In anotherexample the alkaline peroxyacetic acid concentration can be 17 wt % to19 wt % using 30 wt % hydrogen peroxide concentrate 102, 50 wt % sodiumhydroxide as the alkali concentrate 104 and triacetin as the acetyldonor 106.

In step 212, method 200 then stores the resulting combination in peracidholding tank 114. In optional step 210, as indicated by a dashedoutline, method 200 adds additives concentrate 110 to the resultingdiluted peracid from step 208, and then stores the combination inperacid holding tank 114 in step 212. In one embodiment, the alkalineperacid stored in peracid holding tank 114 contains all constituents forformulation of reactive oxygen species output 116 except for the finalactivating pH adjustment. This allows for the diluted alkaline peracid122″ to have a modest lifetime prior to use and be stored in peracidholding tank 114 for several minutes to a few hours, depending on theconcentration determined in step 208, and any additives added in step210. In an alternative embodiment, optional step 210 may be performed byadding an additive concentration 110 of peroxide stabilizer before,during, or after combination of the acyl or acetyl donor 106 in step204.

In step 214, method 200 adjusts the diluted peracid's 122″ pH to theactivated pH level for producing reactive oxygen species output 116 byadding acid concentrate 112 and mixing in mixing chamber 120(3). Theresulting reactive oxygen species output 116 is then distributed to itspoint of use in liquid form. The reactive oxygen species output 116 maythen be used in the form of a liquid, an ice, a foam, an emulsion, amicro-emulsion or an aerosol applied by means such as injection,flooding, spraying, circulation or any other means of conveying a fluid.In one embodiment, the diluted peracid's 122″ pH does not require theaddition of acid concentrate 112 and is ready for immediate distribution214 to its point of use.

In one embodiment, during step 214, an acid concentration 112 iscombined with diluted peracid 122″ such that there is a population ofboth peracetic acid and peracetic acid anion which react together togenerate singlet oxygen according to Equation 3 below:

AcOOH+AcOO⁻→¹O₂+AcOH+AcO⁻  [3]

Wherein the reaction rate for Equation 3 above follows a second orderkinetics and is maximized when the ratio of the two forms ofperoxyacetic acid is equivalent at its pKa of 8.3. The evolution andrelease of singlet oxygen occurs over time ranging from minutes toseveral hours depending on the rate of reaction in Equation 3 above. Inone embodiment, the evolution of singlet oxygen from peroxyacetic acid,or other organic peracid having a similar pKa, the pH is between 6.5 and9.5. In another embodiment the evolution of singlet oxygen fromperoxyacetic acid, or other organic peracid having a similar pKa, may besubstantially retarded between about pH 9.5 and 12.5. For example, as pHbecomes more alkaline the peracetic acid anion dominates the compositionleaving very little peracetic acid to react with by the reaction inEquation 3. Retardation of singlet oxygen production extends thelifetime of the peroxyacetic acid or peracid solution and also allowsfor singlet oxygen use at elevated pH relevant to certain applicationswhich use alkaline oxidants or cleansers up to pH 12 to 12.5.

In optional step 216, as shown by the dashed outline, method 200 furtheractivates the reactive oxygen species output 116 by means of a Fenton orFenton-like catalyst, ultrasound, ultraviolet radiation or thermalactivation (not shown in FIG. 1) to produce radical species such ashydroxyl radicals.

FIG. 3 shows one exemplary system 300 for generation of a concentratedreactive oxygen species output 314 using bulk chemical precursorconstituents, in one embodiment. In one embodiment, concentratedreactive oxygen species output 314 is used in applications where aconcentrate is dosed into a liquid stream, including, but not limited towater and wastewater treatment; cooling tower water treatment andcooling tower system cleaning; desulfurization and deodorization ofgases; water treatment in forestry operations, pulp and paper makingprocesses; oil and gas produced water and hydraulic fracturing flowbackwater treatment. System 300 includes hydrogen peroxide (H₂O₂)concentrate 302, alkali concentrate 304, acyl or acetyl donor 306, acidconcentrate 308, additives concentrate 310, alkaline hydrogen peroxideholding tank 312, reactive oxygen species output 314, pumps 316 andmixing chambers 318. In one embodiment, reactive oxygen species output316 is concentrated singlet oxygen precursor solution.

In one embodiment, alkali concentrate 304 is an aqueous sodium hydroxidesolution. In another embodiment, alkali concentrate is an aqueouspotassium hydroxide solution. Acyl or acetyl donor 306 or mixture ofdonors may be in liquid or solid form, or dissolved in a solvent whenreacted with a solution of hydrogen peroxide.

Acid concentrate 308, for example, includes at least one pH bufferchosen from the group including: weak acid electrolytes includingacetate, citrate, propionate, phosphate and sulfate. Additivesconcentrate 310, for example, includes at least one of the followingadditives chosen from the group including: salts, surfactants,co-solvents, stabilizers, and emulsifiers.

In an embodiment, reactive oxygen species output 314 is a peroxyaceticacid in the absence of hydrogen peroxide and includes at least onechemical precursor species capable of releasing singlet oxygen. Inalternative embodiments, reactive oxygen species output 316 includes twochemical precursor species may be used to release singlet oxygen. In yetanother embodiment, reactive oxygen species output 316 includes morethan two chemical precursor species to release singlet oxygen.

FIG. 4 shows an exemplary method 400 for generating reactive oxygenspecies output 314 using system 300 of FIG. 3. In an embodiment,reactive oxygen species output 316 generated by method 400 isconcentrated singlet oxygen precursor solution. In step 402, an alkalinehydrogen peroxide anion solution 320 is created by mixing H₂O₂concentrate 302 with alkali concentrate 304. For example, molar ratiosof H₂O₂ concentrate 302 to alkali 304 may range from 1:1.2 to 1:2.5. Inone embodiment, a preferred molar ratio range is 1:1.4 to 1:2. In oneembodiment, hydrogen peroxide is a weak acid with a pKa of 11.6 andtherefore its combination with alkali converts it in an acid-baseequilibrium to the hydrogen peroxide anion form as in Equation 1 above.In some embodiments, raising the pH of a hydrogen peroxide solutionenough to put a significant proportion of hydrogen peroxide into theanion form requires an excess of alkali over hydrogen peroxide. Forexample, the molar excess of alkali 304 over H₂O₂ concentrate 302 mayrange from 20% to 100% greater alkali 304. In one embodiment, apreferred molar excess range is 20% to 40% greater alkali 304.

In step 404, the resulting alkaline hydrogen peroxide 320 is stored inalkaline hydrogen peroxide holding tank 312 for immediate or later use.Alkaline hydrogen peroxide 320 has a longer lifetime prior to use whichallows the alkaline hydrogen peroxide 320 to be stored for severalminutes to a few hours in alkaline hydrogen peroxide holding tank 312without as much decomposition as a peracid at a similar concentration.

In step 406, the alkaline hydrogen peroxide 320 is combined with an acylor acetyl donor 306 in mixing tank 318(1) to create a resulting alkalineperacid concentrate 320′. In one embodiment, the acyl or acetyl donor 30is added in proportion to the alkaline hydrogen peroxide 320. In oneembodiment, the molar ratio of H₂O₂ 320 to acyl or acetyl donor 304reactive groups may range from 1:1.25 to 1:4. For example, a preferredmolar ratio range is 1:1.5 to 1:2. In one embodiment, the acyl or acetyldonor is an oxygen-acyl or oxygen-acetyl donor shown in Equation 2aabove, where Ac is acyl [—C(O)R′] or acetyl [—C(O)CH₃] and R and R′ arehydrocarbon-based substituents. In an alternative embodiment, the acylor acetyl donor is a nitrogen-acyl or nitrogen-acetyl donor as shown inEquation 2b above, where Ac is acyl [—C(O)R′] or acetyl [—C(O)CH₃] and Rand R′ are hydrocarbon-based substituents.

In Equations 2a/2b above, the reaction between an acyl or acetyl donor306 and alkaline hydrogen peroxide 320 occurs at alkaline pH bynucleophilic attack of the acyl carbonyl carbon atom by the hydrogenperoxide anion, which displaces the donor molecule fragment as analcohol or amine in a manner analogous to saponification. In someembodiments, the non-equilibrium reactions generalized in Equations2a/2b are conducted between pH 10 and pH 13.

The use of non-equilibrium reaction in Equations 2a/2b provides, forexample, alkaline peracid concentrates 320′ with concentrations of lessthan approximately 5 wt % peroxyacetic acid and other organic peracidsare produced efficiently and rapidly. Using the non-equilibrium reactionallows the hydrogen peroxide residual to be minimized if necessary. Inone embodiment, for example, the peroxyacetic acid water/peroxideconcentration ratios can be 10, 100, or 1000 depending on the ratio ofhydrogen peroxide to acyl or acetyl donor ratio in Equations 2a/2b.

In one embodiment, at least one molar equivalent of acyl or acetyl donor106 is added for each equivalent of hydrogen peroxide in alkalinehydrogen peroxide anion 320 used in Equations 2a/2b to consume all ofthe hydrogen peroxide. In alternative embodiments, excess acyl or acetyldonor 306 reactive groups is necessary to minimize the hydrogen peroxideresidual due to the competing conversion of acyl or acetyl donor 306reactive groups to the corresponding carboxylic acid by the alkaliconcentrate 304 used to raise the pH of the H₂O₂ concentrate 302.

In optional step 408, as indicated by the dashed lines, method 400entrains byproducts 320 produced by the reactions of Equations 2a/2boccurring in step 406. For example, byproducts 322 are entrained insolution with the alkaline peracid concentrate 320′. In one embodiment,byproducts 322 are useful as co-solvents, pH buffers, chelating agentsor stabilizers and carbon substrates for microbial processes after achemical oxidation process. For example, the byproduct 322 of acetyldonors 306 of monacetin, diacetin and triacetin is glycerol, a potentialco-solvent and favorable carbon source for microbes. In anotherembodiment, byproduct 322 of acetyl donor 106 of TAED,diacetylethylenediamine, acts as a chelating agent for transition metalions and potentially serves as a peroxide stabilizer. In yet anotherembodiment, byproduct 322 is the carboxylic acid produced after analkaline peracid concentrate 320′ reacts with a material or decomposes.Alternatively, acetic acid, a byproduct 322 of peroxyacetic acid, servesas a co-solvent, a pH buffer, a chelating agent, and a biologicalsubstrate.

In step 410, method 400 adjusts the alkaline peracid concentrate 320′ pHto the activated pH level for producing reactive oxygen species output314 by adding acid concentrate 308 and mixing in mixing chamber 318(2).The resulting reactive oxygen species output 314 is then distributed toits point of use in liquid form. The reactive oxygen species output 314may then be used in the form of a liquid, an ice, a foam, an emulsion, amicro-emulsion or an aerosol applied by means such as injection,flooding, spraying, circulation or any other means of conveying a fluid.In one embodiment, the alkaline peracid concentrate 320′ pH does notrequire the addition of acid concentrate 308 and is ready for immediatedistribution 410 to its point of use.

In one embodiment, during step 410, an acid concentration 308 iscombined with alkaline peracid concentrate 320′ such that there is apopulation of both peracetic aid and peracetic acid anion which reacttogether to generate singlet oxygen according to Equation 3 above,wherein the reaction rate for Equation 3 above follows a second orderkinetics and is maximized when the ratio of the two forms ofperoxyacetic acid is equivalent at its pKa of 8.3. The evolution andrelease of singlet oxygen occurs over time ranging from minutes toseveral hours depending on the rate of reaction in Equation 3 above. Inone embodiment, the evolution of singlet oxygen from peroxyacetic acid,or other organic peracid having a similar pKa, the pH is between 6.5 and9.5.

In optional step 412, as indicated by a dashed outline, method 400 addsadditives concentrate 310 to the resulting peracid from step 410, andthen distributes the resulting solution for use.

In optional step 414, as shown by the dashed outline, method 400 furtheractivates the reactive oxygen species output 314 by means of a Fenton orFenton-like catalyst, ultrasound, ultraviolet radiation or thermalactivation (not shown in FIG. 3) to produce radical species such ashydroxyl radicals.

Generation of Reactive Oxygen Species Using Electrochemical Generator

In the following embodiments, reactive oxygen species are generated bycreating the necessary constituents and their mixing through thegeneration of all or a portion of these materials on site in a mannerthat minimizes the number of bulk chemical feedstocks and eliminateshazardous bulk chemical feedstocks. For example, the required componentsof hydrogen peroxide, alkali, and acid may be co-generatedelectrochemically from simple feedstocks including water, oxygen gas,and a salt or brine.

In the following embodiments, alternative methods are shown, forexample, for delivering reactive oxygen compositions which can alsogenerate hydroxyl radicals in cases where chlorate and bromate formationis not a primary issue.

FIG. 5 shows an exemplary system 500 for generating chemicals using anelectrochemical reactor 514 and mixing the reactor's 514 outputstogether and optionally with other materials to produce a dilutedreactive oxygen species output 522. In one embodiment, diluted reactiveoxygen species output 520 is used, but not limited to, in applicationswhere a fluid is conveyed to a surface or material as the primaryreactive oxygen species in addition to the parent oxidants at the pointof use or in situ. In some embodiments, applications include, but arenot limited to, in situ chemical oxidation for remediation of soil andgroundwater; ex-situ chemical oxidation for remediation of soil,construction or demolition debris; hard surface cleaning anddecontamination, clean-in place applications in food, dairy, beverageand biopharma production and processing; cleaning of membrane filtrationsystems; and flushing of well casings and water distribution pipes.

System 500 includes an electrochemical reactor 514 including inputs of amakeup water 502(1), brine 504, oxygen gas 506, and power source 508, anacyl or acetyl donor 510, an additives concentrate 512, pumps 516,holding tanks 518, mixing chambers 520, and reactive oxygen speciesoutput 522. In one embodiment, the electrochemical reactor 514 is thatembodied by PCT Application No. PCT/US2012/040325 titled“Electrochemical Reactor and Process.” This published PCT application isincorporated by reference herein in its entirety for its description ofelectrochemical reactors and processes. More specifically, the referenceincludes description for reactor device configurations includingcathodes and anodes which are useful in embodiments of this invention.The reference also includes descriptions of reactors useful forpreparation of oxidants including hydrogen peroxide, superoxide, sodiumhypochlorite, hypochlorites among others and for generation of alkali,and acids. Details of reactor cathodes and anodes and process forproduction of oxidants are also incorporated by reference herein. Anexemplary electrochemical reactor is shown in FIG. 6.

Exemplary Electrochemical Reactor

FIGS. 6A/6B depict an exemplary a cross-sectional view of the generalconfiguration and components of an exemplary electrochemical reactor 600for use in system 500 of FIG. 5, in one embodiment. In one embodiment,electrochemical reactor 600 has a general tubular or annularconfiguration. The housing for electrochemical reactor 600 has threedistinct parts an anode housing 620, a seat plate 634, and an end plate636, each of which may be fabricated in quantity from structuralthermoplastics (pure and filled) including, but not limited to,polyvinyl chloride (PVC), chlorinated polyvinylchloride (CPVC),polyvinylidine difluoride (PVDF), polyethylene, polytetrafluoroethylene(PTFE), ethylene tetrafluoroethyelene (ETFE), acrylonitrile butadienestyrene (ABS) polymer blends, etc.

In an embodiment, anode housing 620 is an extruded tube, such as astandard schedule 80 pipe that is modified with tube fittings,feed-throughs, O-ring, or gasket sealing surfaces and threaded boltholes. In an embodiment, anode housing 620 contains the anolyte solutionwithin electrochemical reactor 600. In an embodiment, anode housing 620contains the anolyte solution within an anolyte chamber 618. In anembodiment, anode housing 620 provides structural integrity toelectrochemical reactor 600 and is what seat plate 634 and end plate 636are fastened to, thereby holding electrochemical reactor 600 and itscontents together as a single unit. In some embodiments, anode housing620 is made from PVC.

In an embodiment, seat plate 634 contains a central opening with atapered surface on which a separator 614 is sealed. A cathode 612extends through seat plate 634. A cathode current distributor andcompression ferrule 630 contacts cathode 612 and anchors it in placewhile simultaneously compressing separator 614 to make a gas-tight sealbetween a cathode flow channel 610 and the anolyte chamber 618. Seatplate 634 also has gasket or O-ring sealing surfaces for makinggas-tight seals with anode housing 620 and with cathode currentdistributor and compression ferrule assembly 630.

In an embodiment, cathode current distributor and compression ferrule630 may be constructed of a rigid material that is conductive andnon-corrosive such as stainless steel alloys, high nickel alloys, andhigh purity titanium, for example. In an embodiment, cathode currentdistributor and compression ferrule 630 is 316 stainless steel. In yetanother embodiment, the surfaces of current distributor and compressionferrule 630 facing into cathode flow channel 610 and manifold are maskedwith a non-conductive material such as a thermoplastic, a polymercoating, or an elastomeric adhesive coating.

In an embodiment, end plate 636 provides a gas inlet 602 and catholytefluid distribution manifolds which are accessed through the catholyteinlet or outlet 608. In an embodiment end plate 636 seals against theend of a gas distributor tube 606 creating a separate gas chamber 604down the center axis of electrochemical reactor 600. End plate 636contains gasket and O-ring sealing surfaces for making gas-tight sealswith gas distributor tube 606 and cathode current distributor andcompression ferrule assembly 630. In an embodiment, end plate 636provides the compressive force to seal separator 614 to seat plate 634,seal seat plate 634 to anode housing 620, seal the faces of the cathodecurrent distributor and compression ferrule assembly 630 to end plate636 and seat plate 634, seal gas distributor tube 606 and fastenelectrochemical reactor 600 together.

In an embodiment, end plate 636 holds the cathode electricalfeed-through posts 632, which contact cathode current distributor andcompression ferrule 630 and are connected by means of conductors to thenegative pole (direct current, DC) or ground (alternating current, AC)of a power supply. In one embodiment, electrical feed-through posts 632are made from a material that is conductive and non-corrosive such asstainless steel alloys, high nickel alloys, and high purity titanium,for example. In an embodiment, cathode electrical feed-through posts 632are 18-8 stainless steel.

In one embodiment, gas distribution tube 606 is a porous or microporousmaterial that allows gas to permeate through its wall and resists waterpermeation. In an embodiment, gas distribution tube 606 is anon-conductive, hydrophobic material such as polyethylene,polypropylene, polytetrafluoroethylene, or polyvinylidene difluoride,for example. In an embodiment, gas distribution tube 606 may be amicroporous ceramic such as alumina, zirconia, titania or other suitablematerial with a hydrophobic coating. Gas distribution tube 606 may bemade by casting-sintering or extrusion production methods, for example.In an embodiment, gas distribution tube 606 contains pores having adiameter rating that is less than about 10 microns. In an embodiment,gas distribution tube 206 contains pores having a diameter rating thatis less than about or equal to 5 microns. The pores of gas distributiontube 606 may be masked in part to bias the gas permeation throughregions of gas distribution tube 606 for purposes including making theends gas and liquid impermeable in the catholyte manifold and currentcollector regions, compensating for pressure gradients, gas loading inthe catholyte, and/or modulating residence time in the cathode flowchamber.

In an embodiment, cathode flow channel 610 is defined by gasdistribution tube 606 and separator 614. Cathode 612 resides withincathode flow channel 610 immersed in the catholyte liquid while gas issupplied from the back side of cathode 612 and the front side of cathode612 faces the separator 614. Cathode 612 may be positioned anywherewithin cathode flow channel 610, including having direct contact withthe separator 614 and/or gas distribution tube 606.

In one embodiment, separator 614 separates the catholyte and anolytefluids from one another, thereby keeping the respective reactants andproducts from mixing in an uncontrolled manner, providing control oftwo-phase fluid dynamics (flow distribution, mixing, electrode contact,partial pressures of gases), preventing undesirable side reactions,preventing electrode shorting or shunt losses, and allowing for precisecontrol of process conditions at each electrode. In an embodimentseparator 614 may be a porous, microporous or nanoporous separatorcomposed of materials including polypropylene, polyethylene,polytetrafluoroethylene, polyvinylidine difluoride, polysulfone,polyethersulfone or a ceramic material (e.g., alumina, zirconia, rareearth oxide, nitride). In an embodiment, separator 614 may be an ionexchange including cation exchange membranes (e.g., perfluorosulfonicacid, sulfonated polyfluorostyrene, sulfonatedpolystyrene-divinylbenzene, perfluorosulfonimide, and perfluorocarboxylate membranes) or anion exchange membranes (e.g., quaternaryammonium polystyrene-divinylbenzene and doped polybenzimidazolemembranes), for example. Separator 614 may be formed into a tubularshape by casting, extrusion, or rolling flat sheets and bonding a seam.In an embodiment, separator 614 is a tubular perfluorosulfonic acidmembrane such as Nafion™.

In an embodiment, cathode 612, also known as a cathode electrode, is ahigh porosity or high surface area material that can conform to atubular shape and be continuously conductive down the length of itsform. Cathode 612 may be a pure metal, an alloy, a conductive polymer, acarbonized or graphitized polymer. In an embodiment cathode 612 has acoating that imparts conductivity, reaction selectivity, catalysis,adsorption, resistance to hydrogen evolution, increased surface area ormodifies wetabiity. In an embodiment, cathode 612 may be made of one ormore porous material formats including sintered or bonded particles,sintered or bonded fibers, woven mesh, continuous fibers or filaments,cloths, felts, and electro-spun or melt-spun filamentous forms. In anembodiment the electrode porosity and pore structure of cathode 612 maybe uniform, graded or random. In an embodiment cathode 612 has anelectrode specific surface area greater than about 10 m² per 1 m²superficial area. In an embodiment cathode 612 has an electrode specificsurface area greater than about 100 m² per 1 m² superficial area. In anembodiment cathode 612 is continuous carbon fibers. The carbon fibersurfaces cathode 612 may be modified to possess carbon oxide species. Inanother embodiment, the carbon fiber surfaces of cathode 612 are coatedwith a catalyst that may be an organic material (e.g., adsorbed orbonded molecules or polymers) or an inorganic material (e.g., adsorbed,bonded or electrodeposited metals, semiconductors, alloys and theiroxide or sulfide derivatives) or a mixture thereof.

In one embodiment, anode 616, also known as an anode electrode, can be adimensionally stable anode consisting of an expanded titanium meshcoated with a catalyst. The catalyst is optimized for oxidation ofspecies in an anolyte solution filling anolyte chamber 618, such aswater or halides or other redox active materials, at reducedoverpotentials or voltage. In some embodiments, the catalyst is aprecious metal, noble metal, platinum group metal or oxides of suchmetals. In an embodiment, the catalyst is iridium oxide.

In an embodiment, anode 616 is in a tubular form, and may be in directcontact with separator 614, and may provide mechanical support toseparator 614. In an embodiment, at least one titanium anode currentcollector tab 626 is affixed to the side of anode 616 and provides apoint of attachment for the anode electrical feed-through post 628,which is also titanium.

In one embodiment, a heat transfer coil, which is not depicted in FIG.6A or FIG. 6B, can be positioned in anolyte chamber 618 withfeedthroughs using two of the anolyte inlet and outlet/vent ports 622and 624, respectively. If required, the heat transfer coil may be usedin the reactor process for cooling or heating the anolyte solution. Inan embodiment, the heat transfer coil is a metal or plastic tube made ofa non-corrosive material such as stainless steel alloys, high puritytitanium, high nickel alloys, polyvinyl chloride, polypropylene,polyvinylidene difluoride, polytetrafluoroethylene. The heat transferfluid circulated through the coil may be water, catholyte solution, gas,air, glycol solutions, for example.

FIG. 7 depicts an embodiment of a reactor system 700 that has a reactorsystem fluid process flow, also known as a flow pathway, that enablesgas recirculation within reactor system 700. A regulated gas makeupstream enters the gas circulation loop through the gas inlet line 702.The gas passes through the gas feed flow control valve 704 and the gasfeed flow meter 706 and then enters the gas chamber 708 of the reactor.At least one boundary of the gas chamber is a gas distributor (notdepicted in FIG. 7, but described above and depicted in FIG. 6 as gasdistributor 606). The gas passes through the gas distributor and intothe cathode chamber 710. Excess gas not consumed in electrochemicalprocess exits cathode chamber 710 co-linearly with liquid catholyte andcathodic products formed through the cathode product line 712. Theliquid and gas mixture passes through a cooling coil 714 prior toentering a gas-liquid separator 716. The separated liquid, which cancontain products formed in cathode chamber 710, is collected in acathode product tank 718. The separated gas flows through a gasrecirculation line 720, through a gas pump 722 and is returned to gasinlet line 702. A portion of the separated gas is removed from thesystem through a gas bleed flow control valve 724 and a gas bleed flowmeter 726. Bleed rate of gas from the system is preferably the same asthe mass flow of the gas makeup stream entering the system less the massconsumption of gas in the reactor less the mass production of gasrecovered from the anode chamber 746 and added to the gas makeup streamthrough an anode gas vent 754.

While gas is passing through the system described in reference to FIG.7, a catholyte solution makeup 730 is added to the cathode feed tank 732where the head space of the tank can be open to the gas makeup streamthrough a gas pressure line 728. In some embodiments, the pneumaticpressure for the gas makeup stream may be used to feed the catholytesolution into cathode chamber 710 of the reactor. In additionalembodiments, the hydraulic pressure of the catholyte solution makeup maybe used to feed the catholyte solution into cathode chamber 710 of thereactor. The catholyte flows from cathode feed tank 732 through thecatholyte inlet line 734, passes through a catholyte flow control valve736 and catholyte flow meter 738 and enters cathode chamber 710 of thereactor. Excess liquid catholyte not consumed in electrochemical processand cathodic products formed exit cathode chamber 710 co-linearly withgas through cathode product line 712. The liquid and gas mixture passesthrough cooling coil 714 prior to entering gas-liquid separator 716. Theseparated liquid, which can contain products formed in cathode chamber710, is collected in cathode product tank 718. The liquid cathodeproduct can be removed from the system during or after operation throughthe cathode product drain 740.

While gas and catholyte is passing through the system described inreference to FIG. 7 an anolyte solution makeup 742 is added to the anodefeed tank 744. The anolyte is supplied through anolyte feed line 746 tothe anode chamber 748 by the action of gravity or a pump (not shown).Excess liquid anolyte not consumed in electrochemical process and anodicproducts formed, including gas, exit the anode chamber collinearlythrough the anode product line 750 and then pass through a gas-liquidseparator 752. The separated liquid is returned to anode feed tank 744while the separated gas is optionally fed to the gas makeup streamthrough anode gas vent 754. Anode gas vent 754 also serves to exposeanode chamber 748 to the gas inlet line pressure such that thedifferential pressure between anode chamber 748 and cathode chamber 710remains constant at any gas inlet line pressure or during pressurefluctuations in the system. The liquid anode or anode product can beremoved from the system during or after operation through the anodeproduct drain 756. While gas, catholyte, and anolyte are passing throughthe system described in reference to FIG. 7 a voltage or current isapplied to the reactor by a controller (not shown in FIG. 6 or 7).

Referring back to FIG. 5, it must be noted that the present embodimentsherein are not limited to only the electrochemical reactor 600 discussedabove, or those disclosed in PCT/US2012/040325; thus, alternativeelectrochemical reactors may be incorporated in the embodiments herein.

In one embodiment, electrochemical reactor 514 creates two outputsincluding alkaline hydrogen peroxide 524 output and acid concentrate 526output, as discussed below with reference to Examples 1-3.

In one embodiment, brine 504 is a solution that contains ions necessaryfor producing alkaline hydrogen peroxide and acids in two separatestreams. The brine 504 may also contain pH buffers and co-solventscompatible with the reaction process, which contribute to the reactiveoxygen species output 522 formulation. For example, pH buffers includeweak chemical electrolytes chosen from the group including: acetate,citrate, propionate, phosphate and sulfate.

Acyl or acetyl donor 510 includes, but is not limited to, an acyl oracetyl donor chosen from the group including: monoacetin, diacetin,triacetin, acetylsalicylic acid, methyl benzoate, ethyl lactate andtetraacetylethylenediamine (TAED). In alternative embodiments, othersynthetic or natural esters, mono-, di- and triacylglycerides andphospholipids having acyl substituents possessing more than one carboncan provide other types of organic peracids by the non-equilibriumreaction mechanism. Acyl or acetyl donor 510 or mixture of donors may bein liquid or solid form, or dissolved in a solvent when reacted with asolution of hydrogen peroxide. Additives concentrate 512, for example,include at least one of the following additives chosen from the groupincluding: salts, surfactants, co-solvents, stabilizers, andemulsifiers.

FIG. 8 shows an exemplary method 800 for generating a diluted reactiveoxygen species output 522 using system 500 of FIG. 5. In step 802,method 800 generates an alkaline hydrogen peroxide 524 output, and anacid concentrate 526 output. Acid concentrate output 526 is then storedin holding tank 518(1). Exemplary processes for generating outputs 524and 526 are discussed below in Examples 1-3. In one embodiment, bothoutput streams 524 and 526 are in concentrated liquid forms produced ata constant rate. For example, the alkaline hydrogen peroxide 524 outputmay contain 0.1 wt % to 3 wt % hydrogen peroxide at pH 12.0 to 13.0.Typical alkaline hydrogen peroxide 524 output may contain 0.3 wt % to0.8 wt % hydrogen peroxide at pH 12.1 to 12.6. The acid concentrate 526output may contain 0.1 wt % to 20 wt % depending on the concentrationand composition of anolyte solution makeup 742. For example, a 20 wt %sodium acetate solution as anolyte solution makeup 742 may produce 13.5wt % acetic acid at 85% conversion efficiency. In an alternativeembodiment, an anolyte solution makeup 742 is a 5 wt % sodium sulfatesolution that may produce 3.6 wt % bisulfate acid at 85% conversionefficiency.

In step 804, the alkaline hydrogen peroxide 524 output is combined withacyl or acetyl donor 510 in mixing tank 520(1) to create alkalineperacid concentrate 524′. In one embodiment, alkaline peracidconcentrate 524′ may be peroxyacetic acid. In one embodiment, the acylor acetyl donor 510 is added in proportion to the hydrogen peroxide 524.In one embodiment, the molar ratio of H₂O₂ 524 to acyl or acetyl donor510 reactive group equivalents may range from 1:1.25 to 1:4. Forexample, a preferred molar ratio range is 1:1.5 to 1:2. If the ratio istoo low a high hydrogen peroxide residual will remain in the peracidconcentrate where it will significantly quench singlet oxygen. If theratio is higher than needed to achieve a low hydrogen peroxide residualthat does not significantly quench singlet oxygen then excess acyl oracetyl donor is remains unused. In one embodiment, the acyl or acetyldonor is an oxygen-acyl or oxygen-acetyl donor shown in Equation 2abelow:

HOO−+AcOR→AcOO−+ROH  [2a]

Where Ac is acyl [—C(O)R′] or acetyl [—C(O)CH₃] and R and R′ arehydrocarbon-based substituents. In an alternative embodiment, the acylor acetyl donor is a nitrogen-acyl or nitrogen-acetyl donor as shown inEquation 2b below:

HOO−+AcNR₂→AcOO−+RNH  [2b]

Where Ac is acyl [—C(O)R′] or acetyl [—C(O)CH₃] and R and R′ arehydrocarbon-based substitutents.

In Equations 2a/2b above, the reaction between an acyl or acetyl donor510 and alkaline hydrogen peroxide 524 occurs at alkaline pH bynucleophilic attack of the acyl carbonyl carbon atom by the hydrogenperoxide anion, which displaces the donor molecule fragment as analcohol or amine in a manner analogous to saponification. In someembodiments, the non-equilibrium reactions generalized in Equations2a/2b are conducted between pH 10 and pH 13.

A particular advantage of the use of non-equilibrium reaction inEquations 2a/2b is that peracid solutions 524″ with concentrations ofless than approximately 5 wt % peroxyacetic acid and other organicperacids can be produced efficiently and rapidly. Using thenon-equilibrium reaction allows the hydrogen peroxide residual to beminimized if necessary. In one embodiment, for example, the peroxyaceticacid water/peroxide concentration ratios can be 10, 100, or 1000depending on the ratio of hydrogen peroxide to acyl or acetyl donorratio in Equations 2a/2b.

In one embodiment, at least one molar equivalent of acyl or acetyl donor510 reactive groups is added for each equivalent of hydrogen peroxide inalkaline hydrogen peroxide anion solution 524 used in Equations 2a/2b toconsume all of the hydrogen peroxide.

In optional step 806, as indicated by the dashed lines, method 800entrains byproducts 528 produced by the reactions of Equations 2a/2b. Inone embodiment, byproducts 528 are entrained in solution with thealkaline peracid concentrate 524′. In one embodiment, byproducts 528 areuseful as co-solvents, pH buffers, chelating agents or stabilizers andcarbon substrates for microbial processes after a chemical oxidationprocess. For example, the byproduct 528 of acetyl donors 510 ofmonacetin, diacetin and triacetin is glycerol, a potential co-solventand favorable carbon source for microbes. In another embodiment,byproduct 528 of acetyl donor 510 of TAED, diacetylethylenediamine, actsas a chelating agent for transition metal ions and potentially serves asa peroxide stabilizer. In yet another embodiment, byproduct 528 is thecarboxylic acid produced after alkaline peracid concentrate 524′ reactswith a material or decomposes. Alternatively, acetic acid, a byproduct528 of peroxyacetic acid, serves as a co-solvent, a pH buffer, achelating agent, and a biological substrate.

In step 808, the resulting alkaline peracid concentrate 524′ is thendiluted with makeup water 502(2) introduced by pump 516(2) to create adiluted peracid 524″ to nearly the point of use concentration and isstored in holding tank 518(2). In optional step 810, as indicated by thedashed outline, additional additives concentrate 512 is combined withdiluted peracid 524″ and then stored into holding tank 518(2).

In step 812, the diluted peracid's 524″ pH is adjusted, by combiningdiluted peracid 524″ with created acid concentrate 526, to the activatedpH level for producing reactive oxygen species output 522 The resultingreactive oxygen species output 522 is then distributed to its point ofuse in liquid form. The reactive oxygen species output 522 may then beused in the form of a liquid, an ice, a foam, an emulsion, amicro-emulsion or an aerosol applied by means such as injection,flooding, spraying, circulation or any other means of conveying a fluid.In one embodiment, the diluted peracid's 524″ pH does not require theaddition of acid concentrate 526 and is ready for immediate distributionto its point of use.

In one embodiment, during step 812, an acid concentration 526 iscombined with diluted peracid 524″ such that there is a population ofboth peracetic aid and peracetic acid anion which react together togenerate singlet oxygen according to Equation 3 below:

AcOOH+AcOO⁻→¹O₂+AcOH+AcO⁻  [3]

Wherein the reaction rate for Equation 3 above follows a second orderkinetics and is maximized when the ratio of the two forms ofperoxyacetic acid is equivalent at its pKa of 8.3. The evolution andrelease of singlet oxygen occurs over time ranging from minutes toseveral hours depending on the rate of reaction in Equation 3 above. Inone embodiment, the evolution of singlet oxygen from peroxyacetic acid,or other organic peracid having a similar pKa, the pH is between 6.5 and9.5.

In optional step 814, as indicated by the dashed outline, the reactiveoxygen species output 522 may further be activated by means of a Fentonor Fenton-like catalyst, ultrasound, ultraviolet radiation, or thermalactivation to produce radical species such as hydroxyl radicals.

FIG. 9 shows an exemplary system 900 for generating chemicals using anelectrochemical reactor 914 and mixing the reactor's 914 outputstogether and optionally with other materials to produce a concentratedreactive oxygen species output 922. In one embodiment, concentratedreactive oxygen species output 922 is used, but not limited to, inapplications where a concentrate is dosed into a liquid stream, which isto be treated or used to distribute the precursor solution throughout alarger system while generating singlet oxygen, for example, as theprimary reactive oxygen species in addition to the parent oxidant(s) atthe point of use or in-situ. In some embodiments, applications includewater and wastewater treatment; cooling tower water treatment andcooling tower system cleaning; desulfurization and deodorization ofgases; water treatment in forestry operations, pulp and paper makingprocesses; oil and gas produced water and hydraulic fracturing flowbackwater treatment.

System 900 includes an electrochemical reactor 914 including inputs of amakeup water 902, brine 904, an oxygen gas 906, and power source 908, anacyl or acetyl donor 910, an additives concentrate 912, holding tanks916, pumps 918, mixing chambers 920, and reactive oxygen species output922. In one embodiment, the electrochemical reactor 914 is that embodiedby PCT Application No. PCT/US2012/040325 titled “Electrochemical Reactorand Process.” An exemplary electrochemical reactor is shown in FIGS.6-7.

In one embodiment, brine 904 is a solution that contains ions necessaryfor producing alkaline hydrogen peroxide and acids in two separatestreams. In one embodiment, brine 904 may contain 5 wt % sodium sulfate.A small fraction of brine 904 may be fed as a side stream to the cathodefeed tank 732 where it is diluted by a factor of 20 with water to 0.25wt % sodium sulfate before being fed to the catholyte inlet line 734 toserve as an electrolyte. The remaining majority of brine 904 is fed tothe anolyte solution makeup 742 and converted to approximately 3.6 wt %sodium bisulfate acid at 85% conversion efficiency. The sodium displacedfrom sodium sulfate is transported from anode to cathode to supportcurrent flow in the reactor and combines with anionic oxygen speciesproduced at the cathode including hydroxide, hydroperoxide andsuperoxide. In an alternative embodiment, all of brine 904 is fed toanolyte solution makeup 742 while a separate brine (not shown) ofdifferent composition and concentration is fed separately into thecatholyte feed tank 732. The brine 904 may also contain pH buffers andco-solvents compatible with the reaction process, which contribute tothe reactive oxygen species output 922 formulation. For example, pHbuffers include weak chemical electrolytes chosen from the groupincluding: acetate, citrate, propionate, phosphate and sulfate.Co-solvents may include a substance chosen from the group including:alcohols such as methanol, ethanol, propanol, propylene glycol, glycolethers, glycerol, ethyl lactate, soybean oil, vegetable oil, sunfloweroil, peanut oil and guar gum.

Acyl or acetyl donor 910 or mixture of donors may be in liquid or solidform, or dissolved in a solvent when reacted with a solution of hydrogenperoxide. Additives concentrate 912, for example, include at least oneof the following additives chosen from the group including: salts,surfactants, co-solvents, stabilizers, and emulsifiers.

FIG. 10 shows an exemplary method 1000 for generating a concentratedreactive oxygen species output 922 using system 900 of FIG. 9. In step1002, method 1000 generates an alkaline hydrogen peroxide 924 output,and an acid concentrate 926 output. Alkaline hydrogen peroxide output924 and acid concentrate output 926 is then stored in separate holdingtanks 916(1), 916(2), respectfully, for immediate or later use. Alkalinehydrogen peroxide 924 has a longer lifetime prior to use which allowsthe alkaline hydrogen peroxide 924 to be stored for several minutes to afew hours in holding tank 916(1) without as much decomposition as aperacid at similar concentration. Exemplary processes for generatingoutputs 924 and 926 are discussed below in examples 1-3. In oneembodiment, both output streams 924 and 926 are in concentrated liquidforms produced at a constant rate.

In step 1004, the alkaline hydrogen peroxide 924 output is combined withacyl or acetyl donor 910 in mixing tank 920(1) to create peracid 924′.In one embodiment, the acyl or acetyl donor is an oxygen-acyl oroxygen-acetyl donor shown in Equation 2a above where Ac is acyl[—C(O)R′] or acetyl [—C(O)CH₃] and R and R′ are hydrocarbon-basedsubstituents. In an alternative embodiment, the acyl or acetyl donor isa nitrogen-acyl or nitrogen-acetyl donor as shown in Equation 2b above.Where Ac is acyl [—C(O)R] or acetyl [—C(O)CH₃] and R and R′ arehydrocarbon-based substituents.

In Equations 2a/2b above, the reaction between an acyl or acetyl donor910 and alkaline hydrogen peroxide 924 occurs at alkaline pH bynucleophilic attack of the acyl carbonyl carbon atom by the hydrogenperoxide anion, which displaces the donor molecule fragment as analcohol or amine in a manner analogous to saponification. In someembodiments, the non-equilibrium reactions generalized in Equations2a/2b are conducted between pH 10 and pH 13.

The use of non-equilibrium reaction in Equations 2a/2b provides peracidsolutions 924′ with concentrations of less than approximately 5 wt %peroxyacetic acid and other organic peracids that are producedefficiently and rapidly. Using the non-equilibrium reaction allows thehydrogen peroxide residual to be minimized if necessary. In oneembodiment, for example, the peroxyacetic acid water/peroxideconcentration ratios can be 10, 100, or 1000 depending on the ratio ofhydrogen peroxide to acyl or acetyl donor ratio in Equations 2a/2b.

In one embodiment, at least one molar equivalent of acyl or acetyl donor910 reactive groups is added for each equivalent of hydrogen peroxide inalkaline hydrogen peroxide anion solution 924 used in Equations 2a/2b toconsume all of the hydrogen peroxide.

In optional step 1006, as indicated by the dashed lines, byproducts 928produced by the reactions of Equations 2a/2b are collected. In oneembodiment, byproducts 928 are useful as co-solvents, pH buffers,chelating agents or stabilizers and carbon substrates for microbialprocesses after a chemical oxidation process. For example, the byproduct928 of acetyl donors 910 of monacetin, diacetin and triacetin isglycerol, a potential co-solvent and favorable carbon source formicrobes. In another embodiment, byproduct 928 of acetyl donor 910 ofTAED, diacetylethylenediamine, acts as a chelating agent for transitionmetal ions and potentially serves as a peroxide stabilizer. In yetanother embodiment, byproduct 928 is the carboxylic acid produced aftera peracid 924′ reacts with a material or decomposes. Alternatively,acetic acid, a byproduct 928 of peroxyacetic acid, serves as aco-solvent, a pH buffer, a chelating agent, and a biological substrate.

In step 1008, the concentrated peracid's 924′ pH is adjusted, bycombining concentrated peracid 924′ with created acid concentrate 926,to the activated pH level for producing reactive oxygen species output922 The resulting reactive oxygen species output 922 is then distributedto its point of use in liquid form. The reactive oxygen species output922 may then be used in the form of a liquid, an ice, a foam, anemulsion, a micro-emulsion or an aerosol applied by means such asinjection, flooding, spraying, circulation or any other means ofconveying a fluid.

In one embodiment, during step 1008, an acid concentration 926 iscombined with concentrated peracid 924′ such that there is a populationof both peracetic aid and peracetic acid anion which react together togenerate singlet oxygen according to Equation 3 above. Wherein thereaction rate for Equation 3 above follows a second order kinetics andis maximized when the ratio of the two forms of peroxyacetic acid isequivalent at its pKa of 8.3. The evolution and release of singletoxygen occurs over time ranging from minutes to several hours dependingon the rate of reaction in Equation 3 above. In one embodiment, theevolution of singlet oxygen from peroxyacetic acid, or other organicperacid having a similar pKa, the pH is between 6.5 and 9.5.

In one embodiment, the concentrated peracid's 924′ pH does not requirethe addition of acid concentrate 926 and is ready for immediatedistribution to its point of use.

In optional step 1010, as indicated by the dashed outline, additionaladditives concentrate 912 is combined with concentrated peracid 924′ andthen distributed as reactive oxygen species output 922 to the point ofuse.

In optional step 1012, as indicated by the dashed outline, the reactiveoxygen species output 922 may further be activated by means of a Fentonor Fenton-like catalyst, ultrasound or ultraviolet radiation to produceradical species such as hydroxyl radicals.

FIG. 11 shows an exemplary system 1100 for generating chemicals using anelectrochemical reactor 1114 and mixing the reactor's 1114 outputstogether and optionally with other materials to produce a superoxidereactive oxygen species output 1122. In one embodiment, the superoxidereactive oxygen species output 1122 is a concentrated superoxideprecursor. Alternatively, the superoxide reactive oxygen species output1122 is a diluted superoxide precursor. In one embodiment, superoxidereactive oxygen species output 1122 is used, but not limited to,applications where a concentrate is dosed into a liquid stream, orapplied to a surface or material. In some embodiments, applicationsinclude water and wastewater treatment; cooling tower water treatmentand cooling tower system cleaning; desulfurization and deodorization ofgases; water treatment in forestry operations, pulp and paper makingprocesses; oil and gas produced water and hydraulic fracturing flowbackwater treatment; in-situ chemical oxidation for remediation of soil andgroundwater; ex-situ chemical oxidation for remediation of soil;construction or demolition debris; hard surface cleaning anddecontamination; cleansing applications in food, dairy, beverage andbiopharma production and processing; cleaning of membrane filtrationsystems.

System 1100 includes an electrochemical reactor 1114 including inputs ofa makeup water 1102(1), brine 1104, an oxygen gas 1106, and power source1108, an additives concentrate 1110, holding tanks 1116, pumps 1118,mixing chambers 1120, and superoxide reactive oxygen species output1122. In one embodiment, the electrochemical reactor 1114 is thatembodied by PCT Application No. PCT/US2012/040325 titled“Electrochemical Reactor and Process.” An exemplary electrochemicalreactor is shown in FIGS. 6-7.

In one embodiment, brine 1104 is a solution that contains ions necessaryfor producing alkaline hydrogen peroxide and acids in two separatestreams. The brine 1104 may also contain pH buffers and co-solventscompatible with the reaction process, which contribute to the reactiveoxygen species output1122 formulation. For example, pH buffers includeweak chemical electrolytes chosen from the group including: acetate,citrate, propionate, phosphate and sulfate. Co-solvents may include asubstance chosen from the group including: alcohols such as methanol,ethanol, propanol, propylene glycol, glycol ethers, glycerol, ethyllactate, soybean oil, vegetable oil, sunflower oil, peanut oil and guargum.

Additives concentrate 1110, for example, include at least one of thefollowing additives chosen from the group including: salts, surfactants,co-solvents, stabilizers, and emulsifiers.

FIG. 12 shows an exemplary method 1200 for generating a concentratedsuperoxide reactive oxygen species output 1122 using system 1100 of FIG.11, in one embodiment. In step 1202, electrochemical generator 1114 isused to create a superoxide solution 1124, as depicted below in example4. In one embodiment, superoxide solution 1124 additionally containshydrogen peroxide co-generated with superoxide. In yet anotherembodiment, in step 1202, electrochemical generator 1114 createssuperoxide solution 1124, with or without co-generation of hydrogenperoxide, and additionally co-generates an acid concentrate 1126. Theproportion of superoxide to hydrogen peroxide co-generated can beadjusted by the nature of the cathode surface. For carbon cathodes, ahigher degree of oxidation of the cathode surface can correlate withhigher superoxide to hydrogen peroxide ratios. Also, when using suchcathodes increasing cathodic current density is correlated withincreasing superoxide to hydrogen peroxide production ratios. The molarratio of superoxide to hydrogen peroxide co-generated by the reactor canrange from approximately 0.01:1 to 10:1. Preferred molar ratios rangesof superoxide to hydrogen peroxide are 0.5:1 to 1.5:1, 1.5:1 to 3:1 and3:1 to 5:1. Electrochemically generated superoxide solutions in theabove ranges are more stable than those solutions generated from bulkchemicals. Superoxide solutions produced from bulk chemicals, atmodestly alkaline pH's, i.e. 11-13 pH, contain HOOH in equilibrium withNaOOH, causing the bulk chemical superoxide solutions to have lessstability. In contrast, electrochemically generated superoxide solutionscan be made to initially contain only NaOOH, which in the presence ofonly NaO₂ and NaOH produces more stable solutions. Upon adding a protonsource, such as an acid, the degradation of electrochemically generatedsuperoxide solutions accelerates.

In alternate embodiments, hydrogen peroxide may be added from anindependent source including bulk chemical concentrate production asdescribed in conjunction with FIGS. 1-4. Superoxide solution 1124 maythen be used as formed, or stored in holding tank 1116(1). Co-generatedacid is stored in holding tank 1116(2).

In step 1204, the superoxide solution 1124 is combined with additives1110, such as salts, co-solvents, or surfactants to increase lifetimeand working time of superoxide formulations; the resulting solution maythen be distributed to its point of use. In step 1206, superoxidesolution 1124 is combined with additives concentrate 1126 to adjust thepH level of the superoxide for pH sensitive applications such asgroundwater and soil remediation. The initial pH can range from pH 8 topH 13. A preferred initial pH range is pH 9 to pH 12. As the superoxidesolution reacts and is consumed, the pH decreases, as shown by thesuperoxide data examples below, leaving a final pH closer to neutral. Instep 1208, the superoxide solution 1124 is diluted with makeup water1104(2) for concentration sensitive applications.

In step 1210, the electrochemical reactor 1114 creates an output of bothhydrogen peroxide and superoxide; method 1200 then generates thehydroperoxyl radical and hydroxyl radical according to the Equations 4-7below.

O₂.⁻+H₂O₂

¹O₂+.OH+OH⁻  [4]

Wherein the Haber-Weiss reaction of Equation 4 between superoxideradical anion and hydrogen peroxide form excited state (singlet)molecular oxygen, hydroxyl radical and hydroxide anion. Hydroxylradicals will react with an excess of hydrogen peroxide in anequilibrium reaction forming water and the hydroperoxyl radical as shownbelow in Equation 5:

⁻OH+H₂O₂→H₂O+HO₂ ⁻  [5]

In one embodiment, hydroperoxyl radicals further subsequently react withexcess hydrogen peroxide to form water, ground state molecular oxygenand hydroxyl radical as shown below in Equation 6:

HO₂.+H₂O₂→H₂O+O₂+.OH  [6]

In step 1210, as the superoxide solution 1124 pH decreases thepopulation of hydroperoxyl radical increases via the equilibrium inEquation 7 below:

HO₂.

O₂.⁻+H⁺  [7]

In one embodiment, hydroxyl radical evolution is most relevant at lowerconcentrations of parent oxidants since hydroxyl radicals rapidly reactwith the parent oxidants. In one embodiment, evolved hydroxyl radicalsinitiate oxidation reactions which the parent oxidants are not capableof, thereby enhancing the oxidative activity.

In yet another embodiment, in step 1212, the superoxide formulation 1124containing hydrogen peroxide may be exposed to a Fenton catalyst,Fenton-like catalyst, ultrasound, ultraviolet radiation, or thermalactivation (not shown in FIG. 11) to produce radical species such ashydroxyl radicals.

Steps 1204-1212 are all optional steps as shown by the dashed outlines.The implementation of steps 1204-1212 depends on the applicationrequired. For example, pH sensitive uses such as soil and groundwaterremediation require diluted superoxide solution 1124, and additionaladditives may be required to be combined with the solution.

In step 1214, the superoxide solution 1124, and any additionalcomponents combined in optional steps 1204-1212 are distributed to thepoint of use. In one embodiment, the point of use is various substratesincluding materials, compounds, atoms or ions (organic or inorganic) tobe reduced, oxidized or degraded and microorganisms to be denatured orkilled. In one embodiment, the superoxide solution 1124 is used soonafter its production due to its relatively short half life determined byinitial concentration, salinity, pH, temperature and other oxidants andconstituents present. In another embodiment, the resulting superoxidesolution as distributed as superoxide reactive oxygen species output1122 is then used in the form of, for example, a liquid, an ice, a foam,an emulsion, a microemulsion or an aerosol applied by means such asinjection, flooding, spraying, circulation or by any other means ofconveying a liquid.

DEFINITIONS

Generally, terms used herein not otherwise specifically defined havemeanings corresponding to their conventional usage in the fields relatedto the invention.

“Reactive Oxygen Species” means a species such as singlet oxygen,superoxide, the hydroxyl radical and the hydroperoxyl radical, forexample. Other reactive oxygen species are known in the art. Reactivespecies are often characterized by their strong oxidizing or reducingactivity, high chemical reactivity and often short or transientlifetimes in aqueous media.

An acyl group, as known in the art, is a —C(O)R′ group, where R is ahydrocarbon-based group. An acetyl group is a type of acyl group whereR′ is a methyl group, i.e., —C(O)CH₃. An “Acyl donor”, particularly an“Acetyl donor” functions to transfer an acyl or particularly an acetylgroup, respectively, to another chemical species as shown in equations2a and 2b above. Acyl or acetyl donors can be oxygen-acyl oroxygen-acetyl donors as shown in Equation 2a or nitrogen-acyl ornitrogen-acetyl donors as shown in Equation 2b above. “Acyl Donor”includes, but is not limited to, an acetyl donor chosen from the groupincluding: monoacetin, diacetin, triacetin, acetylsalicylic acid, andtetraacetylethylenediamine (TAED). Acyl donors that are not acetyldonors include methyl benzoate and ethyl lactate. In alternativeembodiments, “Acyl Donor” may include other synthetic or natural esters,mono-, di- and triacylglycerides and phospholipids having acylsubstituents possessing more than one carbon which provide other typesof organic peracids by the non-equilibrium reaction mechanism.

“Reactive groups” in association with an “acetyl donor” or “acyl donor”distinguish between those acetyl or acyl groups in such donors that willreact with alkaline hydrogen peroxide and those that are non-reactive.One example is TAED, shown below, where only two of the four acetylgroups are reactive.

Another example is triacetin, shown below, where all three acetyl groupsare reactive.

Yet another example is ethyl lactate, shown below, where only one acylgroup is reactive.

“Additives concentrate” or “Additives” means any additional substanceadded to the chemical formulations described herein. “Additivesconcentrate”, or “additives” includes, for example, at least one of thefollowing additives chosen from the group including: salts, surfactants,co-solvents, stabilizers, and emulsifiers, mineral acids, organic acids,alkali, pH buffers, non-oxidizing molecules, ionized molecules andionized atoms.

“Alkali concentrate” or “Alkali” includes any alkali material. In apreferred embodiment, alkali concentrate is an aqueous sodium hydroxidesolution, or an aqueous potassium hydroxide solution.

“Salts” include, for example, at least one salt chosen from the groupincluding: lithium, sodium and potassium chloride; lithium, sodium andpotassium sulfate; calcium chloride or magnesium sulfate below pH 9; andlithium, sodium and potassium salts of acetate, citrate, propionate,phosphate and polyphosphates.

“Surfactants” may be anionic and nonionic for charge compatibility andinclude at least one surfactant chosen from the group including:sulfonic acid salts, alcohol sulfates, carboxylic acid salts, fattyacids, polyether alcohols and sodium dodecyl sulfate.

“Co-solvents” include, for example, at least one co-solvent chosen fromthe group including: alcohols such as methanol, ethanol, propanol,propylene glycol, glycol ethers, glycerol, ethyl lactate, soybean oil,vegetable oil, sunflower oil, peanut oil and guar gum.

“Stabilizers” include, for example, at least one stabilizer chosen fromthe group including: phosphoric acid, phytic acid, tetrasodiumpyrophosphate, sodium hexametaphosphate, sodium tetrametapyrophosphate,ethylenediamine tetraacetic acid and citric acid, chelating agents, andsaline water.

“Emulsifiers” include, for example, at least one foaming and antifoamingagents chosen from the group including: surfactants, oils, co-solventsand polymers including polyethylene glycol.

“Foaming” and “antifoaming agents” include, for example, surfactants,oils, co-solvents and polymers including polyetheylene glycol.

“Byproducts” means any additional substance that results from a chemicalreaction. Byproducts may be useful as co-solvents, pH buffers, chelatingagents or stabilizers and carbon substrates for microbial processesafter a chemical oxidation process. For example, the byproduct ofmonoacetin, diacetin and triacetin is glycerol, a potential co-solventand favorable carbon source for microbes. Another example is thebyproduct of TAED, diacetylethylenediamine, which can act as a chelatingagent for transition metal ions and potentially serve as a peroxidestabilizer. Another example of a byproduct is the carboxylic acidproduced after a peracid reacts with a material or decomposes. Aceticacid, a byproduct of peroxyacetic acid, can serve as a co-solvent, a pHbuffer, a chelating agent, and a biological substrate.

Oxygen-based oxidants have a wide variety of oxidation potentials,reaction pathways, and oxidation kinetics depending on what reactivematerials are present and the conditions they are used in. Because ofthese differences the oxidation products and oxidation byproducts willvary between oxidant type, amount used and other conditions such as pHand temperature. Oxidation products of organic materials are typicallyorganic acid fragments, small organic acids, alcohols and substitutedalkanes. Complete mineralization of organic materials to carbon dioxideand water can occur. Often, the organic oxidation products are morereadily consumed by biological activity than the original materials.

Formation of other undesirable or regulated oxidation byproducts willdepend on both the oxidant and the reactive material(s) present that maybe oxidized. Organic materials possessing nitrogen atoms may be oxidizedand release nitrate as a byproduct. This is a particular issue duringthe oxidation of natural organic material (NOM) such as humic substancesand reduced hydrocarbons from conventional oil reservoirs, oil sands andnatural gas shales.

“Hydrogen Peroxide Concentrate” typically means an aqueous hydrogenperoxide solution. However, in alternative embodiments, hydrogenperoxide concentrate may include other chemical forms of hydrogenperoxide chosen from the group including: calcium peroxide, potassiumperoxide, sodium peroxide, lithium peroxide, percarbonates, andperborates.

“Brine” contains ions necessary for producing alkaline hydrogen peroxideand acids in two separate fluid streams, for example. Brine may also beformulated to contain pH buffers and co-solvents compatible with thegeneration process, which contribute to the hydrogen peroxide solutionformulation.

When a Markush or other grouping is used herein, all individual membersof the group and all combinations and subcombinations possible of thegroup are intended to be individually included in the disclosure. Everyformulation or combination of components described or exemplified can beused to practice the invention, unless otherwise stated.

Without wishing to be bound by any particular theory, there can bediscussion herein of beliefs or understandings of underlying principlesrelating to the invention. It is recognized that regardless of theultimate correctness of any mechanistic explanation or hypothesis, anembodiment of the invention can nonetheless be operative and useful.

One of ordinary skill in the art will appreciate that process methods(adding, mixing, dispensing, etc.), device elements, materials (e.g.,salts, acids, bases, etc.), analytical and spectroscopic methods, andsystem configurations other than those specifically exemplified can beemployed in the practice of the invention without resort to undueexperimentation. All art-known functional equivalents, of any suchmethods, device elements, materials, and configurations are intended tobe included in this invention. Whenever a range is given in thespecification, for example, range of ratios, a temperature range, a timerange, or a composition range, all intermediate ranges and subranges, aswell as all individual values included in the ranges given are intendedto be included in the disclosure.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention in the useof such terms and expressions of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed. Thus, it should be understood that although thepresent invention has been specifically disclosed by preferredembodiments and optional features, modification and variation of theconcepts herein disclosed may be resorted to by those skilled in theart, and that such modifications and variations are considered to bewithin the scope of this invention.

Each reference cited herein is incorporated by reference herein in itsentirety. References can be incorporated by reference herein to provideadditional description of device and system

THE EXAMPLES Example 1 Cogeneration of Alkaline Hydrogen Peroxide andCitric Acid

A reactor system with the reactor of FIG. 6A and fluid process flowillustrated in FIG. 4 was used in this example. The cathode's activesuperficial area was approximately 255 cm². The anolyte reservoir andchamber were charged with a 10% weight to volume solution of trisodiumcitrate in distilled water. A filtered compressed air stream was fedinto the gas feed line at a rate of 5 liters per minute at 1.3 psig. Asolution of 0.05 M sodium sulfate and 0.01 M sodium chloride indistilled water was fed into the catholyte feed line at a rate of 13 mLper minute at approximately 1.0 psig. A DC current was applied to thereactor at 5.0 amps and 4.55-4.65 volts. The catholyte output reached asteady state composition of 720 mg/L hydrogen peroxide with a pH of 12.4(pH measured at a 20-fold dilution) within twelve minutes of applyingthe electric current and remained there at ambient temperature near 15°C. until the process conditions were changed after 29 minutes. The airfeed rate was then increased to ca. 15 liters per minute at 2 psig. Thecatholyte inlet pressure increased to 1.5 psig. The DC current wasmaintained at 5.0 amps while the voltage increased to 4.74 volts. Thecatholyte output reached a new steady state composition of 1040 to 1080mg/L hydrogen peroxide at a pH of 12.3 (pH measured at a 20-folddilution) within five minutes of changing the air feed rate until thereactor was shut down after 46 minutes.

To the existing catholyte feed was added 0.001 M trisodium citrate andthe reactor restarted under the previous process conditions and nearlythe same catholyte output was achieved at 1000-1080 mg/L hydrogenperoxide at a pH of 12.3 decreasing to 12.0 (pH measured at a 20-folddilution) during the first 35 minutes of operation. While maintainingthe current at 5.0 amps (air feed was reduced to 5 liters per minute at46 minutes) the pH of the catholyte output continued to decrease to a pHof 10.2 (not diluted) at 2 hours 25 minutes when the system was shutdown. The anolyte solution was drained from the reactor and had a pH of2.5 indicating the production of citric acid.

Example 2 Generation of Hydrogen Peroxide by Cogeneration of AlkalineHydrogen Peroxide and Sulfate Acids

A reactor system with the reactor of FIG. 6A and fluid process flowillustrated in FIG. 4 was used in this example. The cathode's activesuperficial area was approximately 255 cm². The anolyte reservoir andchamber were charged with a 1.9 L solution of 0.25 M sodium sulfate indistilled water, initial pH=9.5. A ca. 93% oxygen gas stream generatedby a pressure swing adsorption oxygen concentrator was circulatedthrough the gas feed line at a rate of 14.5 liters per minute at 2.9psig. A 0.02 M solution of sodium sulfate in distilled water was fedinto the catholyte feed line at a rate of 12.8 mL per minute at 1.5psig. A DC current was applied to the reactor at 7.0 amps and 3.7 voltsbetween anode and cathode posts. The catholyte output reached a steadystate composition of 2400 to 2450 mg/L hydrogen peroxide at a pH of 12.5within twenty minutes of applying the electric current and remainedthere with an output product temperature of 19 to 20° C. until about 60minutes. Over the following 75 minutes the hydrogen peroxide outputconcentration decreased to about 2000 mg/L with a pH of 12.5 andtemperature increasing to 21° C. The process was shut down after a totaloperating time of 135 minutes. The total collected hydrogen peroxideproduct stream had a volume of 1.7 L with a measured composition of 2300mg/L hydrogen peroxide at pH 12.5. The anolyte was removed from thereactor with a volume of 1.8 L and a measured pH of 1.42 indicatingconversion of sodium sulfate to its acid forms. The hydrogen peroxideand anolyte product streams were combined producing a pH neutralizedproduct with a measured composition of 1050 mg/L hydrogen peroxide at apH of 9.8, 0.2 pH units higher than the starting anolyte solution, and acalculated sodium sulfate content of 0.15 M concentration.

Example 3 Cogeneration of Alkaline Hydrogen Peroxide and SodiumHypochlorite

A reactor system with the reactor of FIG. 6A and fluid process flowillustrated in FIG. 4 was used in this example. The cathode's activesuperficial area was approximately 255 cm². The anolyte reservoir andchamber were charged with a 1.8 L solution of 0.25 M sodium hydroxideand 0.067 M sodium chloride in distilled water, initial pH=13.2. A ca.93% oxygen gas stream generated by a pressure swing adsorption oxygenconcentrator was circulated through the gas feed line at a rate of 14.5liters per minute at 3.0 psig. A 0.02 M solution of sodium sulfate indistilled water was fed into the catholyte feed line at a rate of 12.8mL per minute at 1.7 psig. A DC current was applied to the reactor at7.0 amps and 2.7 volts between anode and cathode posts. The catholyteoutput reached a steady state composition of 2300 to 2450 mg/L hydrogenperoxide at a pH of 12.6 within twenty minutes of applying the electriccurrent and remained there with an output product temperature of 19 to21° C. until the process was shut down after 138 minutes of operation.The final output pH had decreased slightly to 12.5. The total collectedhydrogen peroxide stream had a volume of 1.7 L with a measuredcomposition of 2350 mg/L hydrogen peroxide at pH 12.6. The anolyte wasremoved from the reactor with a volume of 1.75 L and a measured pH of12.0. The total chlorine content was measured to be near 40 mg/L+/−10mg/L.

Example 4 Superoxide Production

Evidence for enhanced superoxide production was observed using theelectrochemical reactor of FIG. 6A and process flow of FIG. 7. At 5 ampsa relatively low hydrogen peroxide production current efficiency of lessthan 60% is accompanied by a lower than normal pH (e.g., 2000-2400 mg/Lhydrogen peroxide and pH 12.40). As the current density is increased to8 amps the hydrogen peroxide production current efficiency decreasesrapidly to less than 40% and the pH decreases by at least 0.1 pH units(e.g., 2600 mg/L hydrogen peroxide and pH 12.26). If the loss ofhydrogen peroxide production efficiency was due to current going intothe four electron reduction of molecular oxygen in Equation 8 below, orthe splitting of water in Equation 9 below, then a significant amount ofhydroxide would be generated thereby raising the pH significantly, whichis not observed.

O₂+H₂O+2e ⁻

HO₂ ⁻+OH⁻  [8]

2H₂O

4e ⁻+O₂+4H⁺  [9]

Furthermore, significant electrolytic splitting of water at the cathodewould require a larger overpotential at the cathode (ca. 0.5 V morenegative) and be reflected in a higher cell voltage. However, the cellvoltage remains unchanged relative to higher efficiencies as in theexamples above.

Additional evidence in support of superoxide production is thedecoloration of methylene blue dye with the fresh cathode outputsolution produced with the above characteristics. A 25 mg/L solution ofmethylene blue can be decolorized to the eye, partially within minutesand completely within 5 hours of mixing with the aforementioned freshlyproduced cathode product (e.g., 2600 mg/L hydrogen peroxide and pH12.26). The decoloration of methylene blue does not occur on this timescale or at all when using catholyte product aged for at least 24 hoursor using store bought hydrogen peroxide to make a simulated catholyteproduct in control experiments. The decoloration of methylene blue dyeis thought to be caused by or at least initiated by the direct action ofgenerated superoxide or by the evolution of hydroxyl radicals via theHaber-Weiss reaction in Equation 4, below, over time relative to thecontrol experiments.

O₂.⁻+H₂O₂=O₂+.OH+OH⁻  [4]

Example 5 Generation of Singlet Oxygen Using Bulk Chemical Precursors

An generation system from FIG. 1 and associated method from FIG. 2 wasused in the present example to show an exemplar of producing a singletoxygen precursor formulation using bulk chemical precursors. A 30 g/Laqueous hydrogen peroxide solution 102 is pH adjusted with sodiumhydroxide alkali concentrate 104 to pH 12.0 to 12.4, using approximately50 g sodium hydroxide per liter of 30 g/L hydrogen peroxide. Theresulting alkaline hydrogen peroxide solution is mixed 120(1) andreacted with an acetyl donor 106 of triacetin in a ratio of 128 gtriacetin per 1 liter alkaline hydrogen peroxide solution. The resultingalkaline peracid concentrate 122′ will contain approximately 65 g/Lperoxyacetic acid and 0.9 g/L hydrogen peroxide assuming 97% conversionof the hydrogen peroxide to peroxyacetic acid. The resulting alkalineperacid concentrate 122′ will also contain about 54 g/L glycerolbyproduct 124.

The peroxyacetic acid concentrate is then diluted to its point of useconcentration before or during pH adjustment to minimize lossesresulting from accelerated peroxyacetic acid decomposition at higherconcentrations when in its activated pH range. In the present example,the above peroxyacetic acid concentrate is diluted to 1.5 g/L, adilution factor of 41.5 times. The peroxyacetic acid solution is dilutedwith 40.5 L of make up water 108 (fresh water or salt water) and thenmixed with an acid concentrate 112 necessary for adjusting the pH toactivate singlet oxygen evolution, where an initial pH range is betweenpH 8 and pH 9. For example, 12 g hydrochloric acid (100% base) is addedper 1 L of concentrate. Additionally, other additives may be added tothe solution by combining them with water 108 used to dilute alkalineperacid concentrate 122′, for example additives such as: sodium orcalcium chloride, tetrasodium pyrophosphate, sodium lauryl sulfate andglycerol.

For the above exemplary singlet oxygen precursor formulation thehydrogen peroxide stock solution, alkali types, and acid types and otheradditives including salts, surfactants, co-solvents, stabilizers, andemulsifiers can be substituted with compatible alternatives known in theart to accommodate specific application requirements. The resultingsinglet oxygen reactive oxygen species output 116 may then be used inthe form of a liquid, an ice, a foam, an emulsion, a microemulsion or anaerosol applied by means such as injection, flooding, spraying,circulation or by any other means of conveying a fluid.

The above example 5 may also be implemented using the system of FIG. 3and method of FIG. 4, without diluting the alkaline peracid concentrate122′.

Example 6 Singlet Oxygen from Electrochemically Generated Chemicals

A generation system from FIG. 5 and associated method from FIG. 8 wasused in the present example to show an exemplar of producing a singletoxygen precursor formulation using an electrochemical generator, in oneembodiment. In the present example of singlet oxygen precursorformulation, the hydrogen peroxide, alkali, and acid may be generatedelectrochemically and on site as an alternative to supplying them asbulk chemicals. Alkaline Hydrogen Peroxide 524 and acid concentrate 526are generated by electrochemical reduction. Electrochemical reduction ofoxygen is conducted at a suitable cathode and water is oxidized at asuitable anode in an electrochemical reactor 514 in which the anode andcathode chambers are separated by a membrane. Oxygen gas 506 and a 4 g/Laqueous sodium acetate solution 504 are supplied to the cathode while 50g/L aqueous sodium acetate solution 504 is supplied to the anode. Adirect current 508 is applied to the electrodes thereby driving thereduction of oxygen at the cathode to produce hydrogen peroxide 524 andsodium hydroxide as the majority products from the cathode while wateris oxidized at the anode to produce acetic acid 526 and oxygen gas asmajority products from the anode.

In this example, the cathode product solution has a composition ofapproximately 6 g/L hydrogen peroxide (as H₂O₂), 4 g/L sodium acetateand a pH of about 12.4 (as NaOH) assuming a 94% current efficiency foroxygen reduction to hydrogen peroxide. The anode product solution has acomposition of approximately 31 g/L acetic acid and 7/5 g/L sodiumacetate assuming an 85% sodium acetate to acetic acid conversion. Theanode product solution volume is about 0.46 L per 1 L of cathode productsolution.

The alkaline hydrogen peroxide cathode product solution is mixed andreacted with an acyl or acetyl donor 510, for example, triacetin in aratio 25.5 g triacetin per 1 liter of alkaline hydrogen peroxidesolution 524. The resulting concentrate will contain approximately 13g/L peroxyacetic acid 524′ and 0.17 g/L hydrogen peroxide assuming 97%conversion of the hydrogen peroxide to peroxyacetic acid. Theconcentrate will also contain about 11 g/L glycerol byproduct 528.

In the present example, the above peroxyacetic acid concentrate 524′ isdiluted to 1.5 g/L, a dilution factor of 8.7 times. Dilution is achievedby diluting the acidic anode product solution with 7.24 L of water502(2) (fresh water or salt water). Additional additives 512 are alsoadded, such as sodium or calcium chloride, tetrasodium pyrophosphate,sodium lauryl sulfate, and glycerol. The solution is then combined withacid concentrate 526 to produce a singlet oxygen reactive oxygen speciesoutput 522 with a pH in the range of pH 8 and pH 9.

For the above exemplary singlet oxygen precursor formulation thehydrogen peroxide stock solution, alkali types, and acid types and otheradditives including salts, surfactants, co-solvents, stabilizers, andemulsifiers can be substituted with compatible alternatives known in theart to accommodate specific application requirements. The resultingsinglet oxygen reactive oxygen species 522 may then be used in the formof a liquid, an ice, a foam, an emulsion, a microemulsion or an aerosolapplied by means such as injection, flooding, spraying, circulation orby any other means of conveying a fluid.

The above example 6 may also be implemented using the system of FIG. 9and method of FIG. 10, without diluting the peroxyacetic acidconcentrate 524′.

Example 7 Electrochemical Generation of H₂O₂ as “Control” for SuperoxideProduction Experiments (Experiments 8-9)

A reactor system with an electrochemical reactor of FIG. 6 and fluidprocess flow illustrated in FIG. 7 was used in this example. A carbonfiber cathode suitable for high efficiency hydrogen peroxide productionwas installed in the reactor with an active superficial area of 255 cm².The anolyte reservoir and chamber were charged with a 2.5 L solution ofabout 1.5 M sodium hydroxide in distilled water. The anolyte wasrecirculated through the anode chamber over time. A ca. 93% oxygen gasstream generated by a pressure swing adsorption oxygen concentrator atabout 5 L per minute was circulated through the gas feed line andreactor by a pump at a rate of 10 liters per minute at 2.6 psig while a5 L per minute bleed stream of oxygen gas was released from the system.The catholyte was a 0.05 M solution of sodium sulfate in distilled wateradjusted to pH 11.2 with sodium hydroxide to precipitate trace magnesiumin the electrolyte. The catholyte solution was fed into the catholytefeed line at a rate of 12.8 mL per minute at 1.3 psig (single pass, flowthrough). A DC current was applied to the reactor at 5.0 amps (currentcontrol). The negative pole of the power supply was grounded. Hydrogenperoxide concentration was analyzed by titration using the Hach Inc.HYP-1 Hydrogen Peroxide Test and pH was measured using an Oakton pH 11Series meter with a temperature compensated double junction pHelectrode.

The catholyte output reached a steady state composition of 3700+/−50mg/L hydrogen peroxide and pH 12.25+/−0.04 at 25 to 26° C. The currentefficiency for hydrogen peroxide production was calculated to be 90.8%assuming a two electron reduction of molecular oxygen.

Example 8 Superoxide Generation Using Electrochemical Reactor

A generation system from FIG. 11 and associated method from FIG. 12 wasused in the present example to show an exemplar of producing asuperoxide precursor formulation using an electrochemical generator, inone embodiment. Superoxide concentrate 1124 and, optionally, acidconcentrate 1126 are electrochemically generated using anelectrochemical reactor 1114. Electrochemical reduction of oxygen isconducted at a suitable cathode and water is oxidized at a suitableanode in an electrochemical reactor 1114 in which the anode and cathodechambers are separated by a membrane. Oxygen gas 1106 and a 4 g/Laqueous sodium acetate solution 1104 are supplied to the cathode while a50 g/L aqueous sodium acetate solution 1104 is supplied to the anode. Adirect current 1108 is applied to the electrodes thereby driving thereduction of oxygen at the cathode to produce superoxide, hydrogenperoxide and sodium hydroxide as the majority products 1124 of thecathode, while water is oxidized at the anode to produce acetic acid andoxygen gas as the majority products 1126 of the anode.

In this example the cathode product solution 1124 has a composition ofapproximately 3.0 g/L superoxide (as O_(2*) ⁻), 3.2 g/L hydrogenperoxide (as H₂O₂), 4 g/L sodium acetate and a pH of about 12.2 (asNaOH) assuming a 90% current efficiency for oxygen reduction tosuperoxide and hydrogen peroxide. The anode product solution 1126 has acomposition of approximately 31 g/L acetic acid and 7.5 g/L sodiumacetate assuming 85% sodium acetate to acetic acid conversion. The anodeproduct solution volume is about 0.46 L per 1 L of cathode productsolution.

The superoxide-containing cathode product solution 1124 is then dilutedto its point of use concentration before or during pH adjustment tominimize losses resulting from accelerated superoxide decomposition atlower pH. In this example the superoxide is diluted to 1.0 g/L, adilution factor of 3 times. In one example, dilution can be achieved bydiluting the acidic anode product solution with 1.54 L of water (freshwater or salt water), adding other desirable additives to the dilutedanode product solution and then combining the diluted anode productsolution with the superoxide-containing cathode product solution.Examples of additives include sodium chloride, sodium lauryl sulfate,isopropanol and soybean oil.

Due to the decreasing lifetime of superoxide in aqueous media as the pHbecomes less alkaline, non-aqueous co-solvents or emulsion compositionsmay be employed to improve the lifetime and activity of superoxidesolution 1124. Alternatively, the alkaline superoxide-containing cathodeproduct solution may be utilized directly, followed by pH neutralizationor adjustment with the acidic anode product solution.

For the above formulation the hydrogen peroxide stock solution, alkalitypes, and acid types and other additives including salts, surfactants,co-solvents, stabilizers, and emulsifiers can be substituted withcompatible alternatives known in the art to accommodate specificapplication requirements. The resulting singlet oxygen reactive oxygenspecies 1122 may then be used in the form of a liquid, an ice, a foam,an emulsion, a microemulsion or an aerosol applied by means such asinjection, flooding, spraying, circulation or by any other means ofconveying a fluid. The above example may also be implemented withoutdiluting the superoxide solution 1124.

Example 9 Dye Oxidation with Singlet Oxygen

Methylene blue (MB) is a heterocyclic aromatic compound with themolecular formula C₁₆H₁₈N₂SCl and is considerably resistant tooxidation. MB is a useful model dye for comparing the oxidativestrengths of various oxidizers based on the rate of color loss fromsolutions when treated. Methylene blue dissolved in water has an intenseabsorption band maximum near 662 nm in the visible part of theelectromagnetic spectrum resulting in its intense blue color. Observingthe loss of this absorption and blue color by oxidation of the dyeprovides a preliminary comparison between oxidizers.

A series of MB oxidation trials were conducted near room temperature(17-22° C.) by combining equal volumes of oxidant formulations with 100mg/L MB stock solution resulting in a 50 mg/L MB initial concentration.The change in MB solution color was evaluated over time by visualcomparison to a series of color standards made by serial dilution of thesame 100 mg/LMB stock solution. Color standards were 50, 25, 10, 5, 1,and 0.5 mg/L MB. Color comparisons were made with test samples and colorstandards contained in 12 mm inner diameter Pyrex test tubes positionedin front of a back-lit, diffuse white field. Solution pH and temperaturewas measured with a temperature compensated pH electrode using an OaktonpH11 meter with three point calibration. Hydrogen peroxide concentrationwas measured using the HACH hydrogen peroxide test method based on theammonium molybdate-catalyzed triiodide titration with sodiumthiosulfate.

The following bulk chemical reagents were purchased and used asreceived: Triacetin, 99%, bought from Acros Organics; Methylene Blue, 1%w/v aqueous solution bought from Ricca Chemical Company; Hydrogenperoxide, 2.7% w/v (measured) bought from Kroger Co.; Sodium Hydroxide,100% bought from Rooto Corp.; Sodium Sulfate, 100% anhydrous bought fromDuda Diesel; and Distilled water from Kroger Co.

For example, electrochemically generated hydrogen peroxide concentratesolution was produced one to three days prior to use and stored at 2-4°C. in a high density polyethylene bottle. The composition of theelectrochemically generated hydrogen peroxide solution in distilledwater at room temperature was 4800 mg/L (+/−50 mg/L) hydrogen peroxide,pH 12.81 (+/−0.04) as sodium hydroxide, and 7.1 g/L sodium sulfate.Hydrogen peroxide concentration was stable for several days.

Electrochemically co-generated sulfate acid concentrate with pH 1.40(+/−0.04) was produced from a 0.31 M (44.0 g/L) sodium sulfate brine indistilled water. The approximate calculated composition of the acidconcentrate at 20° C. (pKa≈0.973) was 0.091 M sodium sulfate and 0.24 Msodium bisulfate.

Peroxyacetic acid formulations were made by mixing electrochemicallygenerated hydrogen peroxide solution with tiacetin as the acetyl donor.The molar ratios of hydrogen peroxide:acetyl donor group was adjusted toproduce non-equilibrium perxyacetic acid solutions. The triacetinmolecule possesses three molar equivalents of acetyl groups. A 2.00 mLvolume of the oxidant formulation was combined with 2.00 mL of 100 mg/LMB aqueous solution. The initial pH was then adjusted by quicklytitrating in electrochemically generated sulfate acid concentrate inamounts less than 0.5-2% of the total solution volume. The initialconcentration of peroxyacetic acid was estimated based on the initialhydrogen peroxide concentration. The amount of unreacted hydrogenperoxide residual was not measured, but its effect was observed in thepercent color removal results.

Table 1 below represents examples of MB oxidation test resultsdemonstrating the relative effects of oxidant, pH, concentration andmolar ratio of acetyl donor groups reacted with hydrogen peroxide. Theinitial MB concentration was 50 mg/L in all cases. Entry 1 usedcommercially produced hydrogen peroxide as the parent oxidant nearneutral pH without adjustment. Entry 2 used electrochemically generatedhydrogen peroxide at high strength without pH adjustment. Entry 3 usedcommercially produced hydrogen peroxide which was reacted with triacetinnear pH 12.2, a known amount of hydrogen peroxide was added and then pHwas adjusted with electrochemically generated sulfate acid concentrate.Entries 4-13 used electrochemically generated hydrogen peroxide reactedwith triacetin and diluted to varying initial concentrations ofperoxyacetic acid as the parent oxidant.

TABLE 1 MB Oxidation Test Results Molar Entry reaction ratio, InitialConc., Final % Color no. HP:acetyl equiv. Parent Oxidant Initial pHFinal pH Time (h) Removal 1 1:0 50 mg/L, HP 6.1-6.4 NR 3 0 2 1:0 2150mg/L, HP 12.0-12.2  NR 3 0 3 1:2 7000 mg/L, PAA 9.00 NR 48 <10 5000mg/L, HP 4 1:1 <240 mg/L, PAA 3.54 3.71 7 0 5 1:1 <240 mg/L, PAA 8.556.93 7 25 6 1:2 240 mg/L, PAA 4.50 4.55 8 0 7 1:2 240 mg/L, PAA 9.007.90 8 65 8 1:4 240 mg/L, PAA 4.60 4.73 7 0 9 1:4 240 mg/L, PAA 8.497.75 7 50 10 1:2 465 mg/L, PAA 3.97 3.70 7 20 11 1:2 465 mg/L, PAA 9.017.99 7 82 12 1:2 950 mg/L, PAA 9.01 8.16 7 93 13 1:2 1900 mg/L, PAA 9.008.46 5 99.5 HP = hydrogen peroxide; PAA = peroxyacetic acid; NR = notrecorded

The above results demonstrate, for example, that singlet oxygen evolvingformulations are significantly stronger oxidants than hydrogen peroxideor peroxyacetic acid solutions alone. Hydrogen peroxide by itself didnot have any observed effects during this test and after the testsolution in Entry 1 had sat for several days. Alkaline hydrogen peroxidein Entry 2 eventually caused a small amount of MB to precipitate afterseveral hours more and has a slight shift in solution color to ta purplehue, but color loss did not progress significantly. A control test with50 mg/L MB without any oxidant, but in the presence of 1 M sodiumhydroxide gave a similar result to Entry 2 indicating that hydrogenperoxide had little or no effect on the observed changes. Entry 3demonstrates that the presence of a significant concentration ofhydrogen peroxide in the peroxyacetic acid formulation severely inhibitsoxidative activity toward MB and color removal.

Entries 5, 7 and 9 in Table 1, above, demonstrate the effect ofHP:acetyl donor equivalent ratio on oxidation activity as impacted byhydrogen peroxide residual, which leads to inhibited oxidative activitypresumably due to singlet oxygen quenching. When the HP:acetyl donorequivalent ratio is 1:1 the MB color loss is significantly lower thanwhen the ratio is 1:2 or 1:4. The difference in results betweenHP:acetyl donor equivalent ratios of 1:2 and 1:4 is minimal whennormalized to reaction time indicating that an excess of acetyl donor isnot necessarily detrimental to oxidative activity.

When the initial peroxyacetic acid solution pH was above 8 in Table 1,above, the oxidation and color loss of MB was observed. When the initialperoxyacetic acid solution pH was below 5 there was little to no colorloss observed. When the pH remained above approximately 6.5 an increasein the peroxyacetic acid concentration resulted in faster and greatercolor loss of MB. This trend is demonstrated by the results in graph1300 of FIG. 13 showing the percent color removal of 50 mg/L MBsolutions observed over time starting with different initialperoxyacetic acid concentrations. The results in graph 1300 of FIG. 13also demonstrate that the singlet oxygen evolution occurs over a periodof several hours. This result is reinforced by the observation of gasbubble evolution, which persists for several hours when the initialperoxyacetic acid concentrations are significantly greater than 1900mg/L.

Example 10 pH Control and Formulation of Nitrate Oxidation Byproduct

As materials are oxidized and the peroxyacetic acid transforms to aceticacid the pH of the treatment solutions decreases. The initial pH and/orpH buffer concentration of the singlet oxygen precursor solutions shouldbe adjusted to control the change in pH during the active oxidationperiod such that the final pH is in a desirable range. Table 2 belowshows oxidation results for the raw hydraulic fracturing and flowbackwater with singlet oxygen precursor formulations. Data Table 2, below,demonstrates how the initial pH and amount of parent oxidant and amountof oxidation can be used control the final pH of the oxidized water.This example also illustrates the production of nitrate as a byproductof oxidation of nitrogen-containing organic materials with singletoxygen formulations.

TABLE 2 Oxidation Results For Raw Hydraulic Fracturing and FlowbackWater PAA: Raw Total Final TOC water oxidation Initial (6 h) NitrateSample mass volume volume oxidation oxidation byproduct No. ratio (mL)(mL) pH pH (mg/L) 1   0:1 37 56.7 8.19 8.19 BDL 2 2.4:1 37 56.7 8.876.73 0.92 3 1.2:1 37 56.7 8.77 6.81 0.52 4 0.6:1 37 56.7 8.67 7.00 0.31BDL = below detection limit of 0.1 mg/L

Raw hydraulic fracturing and flowback water generated by oil and gasdevelopment operations was obtained from an undisclosed location inColorado, USA after temporary impoundment in a lagoon. The compositionof the raw water was approximately 5000 mg/L total organic carbon(hereinafter “TOC”), approximately 10,000 mg/L total dissolved solids(hereinafter “TDS”), appeared opaque with suspended silt and dark brownorganic material and had a pH of 8.19 indicating alkalinity content. Theraw water also possessed a mild odor of volatile organic compounds(i.e., petrochemicals).

Singlet oxygen formulation concentrate, formulated by the aboveembodiments, was added to the raw water in varying amounts withdistilled water added to maintain equivalent dilutions between samples.The approximate mass ratios of peroxyacetic acid to TOC are reported inTable 2, above, to distinguish singlet oxygen precursor doses. Thesinglet oxygen precursor formulation was made by mixing and reacting1.40 mL triacetin with 16.3 mL of a 1% w/v hydrogen peroxide stocksolution adjusted to pH 12.40 with NaOH. The resulting peroxyacetic acidsolution concentrate was adjusted to pH 8.9 with about 2.0 mL ofelectrochemically generated sulfate acid concentrate of pH 1.32. Thesamples in Table 2, above, were prepared by mixing 37 mL of raw waterwith: 19.7 mL of distilled water for control sample no. 1; 19.7 mL ofsinglet oxygen precursor formulation for sample no. 2; 9.8 mL of singletoxygen precursor formulation plus 9.8 mL distilled water for sample no.3; 4.9 mL of singlet oxygen precursor formulation plus 14.8 mL distilledwater for sample no. 4. The samples were each contained in 100 mL glassjars at room temperature.

The initial pH was measured immediately after sample preparation. Theinitial pH was affected by the amount of singlet oxygen precursorformulation added to the sample. Samples containing singlet oxygenprecursor formulation evolved gas rapidly enough to effervesce for 1-2hours. Effervescence also served as an effective mixing mechanism.Within the first 30 minutes of oxidation the color of sample no's 2-4had become paler than the control sample no. 1. After 5-6 hours visiblegas evolution had subsided and the oxidized samples were a significantlypaler tan color than the control. Sample no. 2 was the palest in colorcorresponding with the greatest singlet oxygen precursor dose.

The final pH was measured at 6 hours. Higher initial singlet oxygenprecursor formulation concentration led to lower final pH. Oxidizedsamples had a final pH of 6.7 to 7.0 demonstrating the potential tobalance pH with the singlet oxygen precursor formulation and dose. Theprecursor formulation used in this example contained acetate and aceticacid which can act as a pH buffer and reduce alkalinity, respectively.As oxidation proceeded, additional acetic acid (the byproduct fromperoxyacetic acid reactions) and potentially partial oxidation productswith carboxylic acid groups accumulated leading to a decrease in pH overtime.

Nitrate was found to be an oxidation byproduct of the organic materialin the hydraulic fracturing flowback water. Results of ionchromatography analysis of the samples in Table 2, above, corrected fordilution, show that byproduct nitrate content was proportional tosinglet oxygen precursor formulation concentration. Nitrogen-containingmaterials such as natural organic materials were oxidized enough toliberate nitrogen as nitrate. Nitrate was not detected in thenon-oxidized raw water.

In view of the many possible embodiments to which the principles of thedisclosure may be applied, it should be recognized that the embodimentsherein should not be taken as limiting the scope of the presentdisclosure.

Example 11 Electrochemical Co-Generation of Hydrogen Peroxide andSuperoxide

A reactor system with an electrochemical reactor of FIG. 6 and fluidprocess flow illustrated in FIG. 7 was used in this example. A carbonfiber cathode suitable for combined hydrogen peroxide and superoxideproduction was installed in the reactor with an active superficial areaof 255 cm². The anolyte reservoir and chamber were charged with a 2.5 Lsolution of about 1.5 M sodium hydroxide in distilled water. The anolytewas recirculated through the anode chamber over time. A ca. 93% oxygengas stream generated by a pressure swing adsorption oxygen concentratorat 5 L per minute was circulated through the gas feed line and reactorby a pump at a rate of 9.0 liters per minute at 3.0 psig while a 5 L perminute bleed stream of oxygen gas was released from the system. Thecatholyte was a 0.05 M solution of sodium sulfate in distilled wateradjusted to pH 11.2 with sodium hydroxide to precipitate trace magnesiumin the electrolyte. The catholyte solution was fed into the catholytefeed line at a rate of 12.8 mL per minute at 1.6 psig (single pass, flowthrough). A DC current was applied to the reactor at either 5.0 amps or8.0 amps (current control). The negative pole of the power supply wasgrounded. Hydrogen peroxide concentration was analyzed by titrationusing the Hach Inc. HYP-1 Hydrogen Peroxide Test and pH was measuredusing an Oakton pH 11 Series meter with a temperature compensated doublejunction pH electrode.

At 5.0 amps operating current the catholyte output reached a steadystate composition of 2000+/−50 mg/L hydrogen peroxide and pH12.20+/−0.04 at 25 to 27° C. The current efficiency for hydrogenperoxide production was calculated to be 48.4% assuming a two electronreduction of molecular oxygen. A maximum potential concentration ofsuperoxide anion produced was calculated to be 3400 mg/L assuming 90% ofthe balance of the applied current caused the one electron reduction ofmolecular oxygen.

At 8.0 amps operating current the catholyte output reached a steadystate composition of 2500+/−50 mg/L hydrogen peroxide at 27 to 28° C.and pH 12.58+/−0.04 measured at a 10-fold dilution to adjust the pH towithin the accurate range of the pH probe. The current efficiency forhydrogen peroxide production was calculated to be 37.8% assuming a twoelectron reduction of molecular oxygen. A maximum potentialconcentration of superoxide anion produced was calculated to be 6800mg/L assuming 90% of the balance of the applied current caused the oneelectron reduction of molecular oxygen.

Analysis of Electrochemically Generated Hydrogen Peroxide and SuperoxideExamples 7 and 11

Catholyte outputs from Examples 7 and 11 above were analyzed byultraviolet-visible absorption spectroscopy between 21 and 24° C. Datawas collected using an Ocean Optics USB4000-UV-VIS absorbance system(200-850 nm) with SpectraSuite software. Disposable 1 cm Plastibranddisposable macro cuvettes were used with a 220 nm cutoff. Hydrogenperoxide concentration was analyzed by titration using the Hach Inc.HYP-1 Hydrogen Peroxide Test and pH was measured using an Oakton pH 11Series meter with a temperature compensated double junction pHelectrode. All samples were diluted with distilled water to 100 mg/Lhydrogen peroxide and pH adjustments were made using sodium hydroxide orpH 1.40 sodium bisulfate solution. Hydrogen peroxide UV standards weremade from 3% topical hydrogen peroxide and sodium hydroxide combined indistilled water. Standards included 100 mg/L hydrogen peroxide at pH6.7, 10.0, 11.0 and 12.0. Standards were also made with 0.10 mol/L NaOH(nominally pH 13) and 1.0 mol/L NaOH (nominally pH 14) measured byweight of sodium hydroxide dissolved in distilled water at roomtemperature.

The previously reported absorption band maximum for dilute aqueoussuperoxide generated by radiolysis of dissolved oxygen in the presenceof sodium formate and ethylenediaminetetraacetic acid at pH 10.5 was 245nm. See “Reactivity of HO₂/O₂ ⁻ Radicals in Aqueous Solution,” Beilski,et al., J. Phys. Chem. Ref. Data, Vol. 14, No. 4, 1985. The reportedabsorption band maximum for dilute hydroperoxyl radical (HO₂*) inaqueous perchloric acid at pH 1.5 was 225 nm.

FIGS. 14A/B shows graphs 1400, 1450 that compares the UV absorbancespectra of fresh catholyte outputs, within 2 minutes of production, ofthe high efficiency hydrogen peroxide output 1402 in Example 7, and theco-generated hydrogen peroxide and superoxide output 1404 in Example 11.Both outputs were produced at 5 amps.

FIG. 14A shows graph 1400 that shows the full spectra of samples dilutedto 100+/−4 mg/L hydrogen peroxide and adjusted to pH 12.00+/−0.04 andgraph 1450 of FIG. 14B shows the same spectra with hydrogen peroxideabsorbance subtracted off. The co-generated hydrogen peroxide andsuperoxide output exhibits additional absorbance intensity on theshorter wavelength side of the hydrogen peroxide band and a weakabsorbance band in the subtracted spectrum. The high efficiency hydrogenperoxide output did not exhibit a second absorbance band aftersubtracting off the hydrogen peroxide absorbance. Hydrogen peroxide at100+/−4 mg/L and pH 12.0 has an absorbance maximum near 232 nm while theweak absorbance band of the co-generated hydrogen peroxide andsuperoxide output is shifted to shorter wavelength.

The weak absorbance band of the co-generated hydrogen peroxide andsuperoxide output increases in intensity over time at pH 12, which isbehavior not observed for alkaline hydrogen peroxide alone.

FIGS. 15A/B show graphs 1500, 1550 that show the evolution of the UVabsorbance spectrum over five hours for the co-generated hydrogenperoxide and superoxide output produced at 8 amps in Example 11 dilutedto 100+/−4 mg/L hydrogen peroxide, adjusted to pH 12.00+/−0.04 andanalyzed over time. Graph 1500 shows the full spectra of the outputincluding hydrogen peroxide at two minutes after production 1502, threehours after production 1504 and five hours after production 1506. Graph1550 shows the same spectra with hydrogen peroxide absorbance subtractedoff at two minutes after production 1552, three hours after production1554, and five hours after production 1556. The growing band in graph1550 has an absorbance maximum near 224 nm at five hours, which isconsistent with the reported position of the hydroperoxyl radical. Theoriginal spectrum in graph 1500 shows an 18% decrease in absorbance anda shift in the absorbance band maximum from 230 nm, to 228 nm at threehours, to 226 nm at five hours. These spectral changes were accompaniedby a decrease in pH to 11.66+/−0.04, but there was no measurabledecrease in hydrogen peroxide concentration. The aforementioned behavioris consistent with the buildup of a different species with lower molarabsorptivity by a slow chemical reaction or equilibrium process and aslow loss of a non-hydrogen peroxide species in the electrochemicallygenerated output.

For comparison, the same output produced at 8 amps in Example 11,diluted to 100+/−4 mg/L hydrogen peroxide and adjusted to pH 13 (0.10mol/L NaOH) did not exhibit any change in the 224 nm hydrogen peroxidesubtracted peak intensity or hydrogen peroxide concentration over 5hours (data not shown). The original spectra did show a 10% decline inpeak intensity of the hydrogen peroxide peak near 231 nm over five hourswithout any wavelength shift in peak maximum position. This behaviorshows a more stable output solution with a slower loss of a non-hydrogenperoxide species in the electrochemically generated output.

FIGS. 16A/B show graphs 1600, 1650 that shows the evolution of the UVabsorbance spectrum over five hours for the co-generated hydrogenperoxide and superoxide output produced at 8 amps in Example 11 dilutedto 100+/−8 mg/L hydrogen peroxide, adjusted to pH 11.04+/−0.04 andanalyzed over time. Graph 1600 shows the full spectra of the outputincluding hydrogen peroxide at two minutes after production 1602, oneand a half hours after production 1604 and five hours after production1606. Graph 1650 shows the same spectra with hydrogen peroxideabsorbance subtracted off at two minutes after production 1652, one anda half hours after production 1654, and five hours after production1656. The 221 nm band in graph 1650 increases in intensity for a periodof time, then decreases in intensity. The original spectrum in graph1600 shows a 56% decrease in absorbance and a shift in the absorbanceband maximum from 225 nm to 222 nm at five hours. These spectral changeswere accompanied by a decrease in pH to 9.47+/−0.04 and a 20% decreasein hydrogen peroxide concentration to 80+/−4 mg/L. Approximately 55-60%of the decrease in absorbance in graph 1600 is attributable to thedecrease in pH. In graph 1650 the initial spectrum of the output shows abroad absorption shoulder in the 240 to 260 nm region, which isconsistent with the absorption region for the “free” form of dilute,aqueous superoxide. This shoulder is often observed for freshly madereactor output solutions. These results show that a lower initial pHleads to a more reactive and less stable output solution including theformation of a different species with lower molar absorptivity thanhydrogen peroxide; a more rapid loss of this different species involvingthe consumption of hydrogen peroxide; and a more rapid loss of anon-hydrogen peroxide species in the electrochemically generated output.

The UV spectra of co-generated hydrogen peroxide and superoxide outputsshow that the initially generated alkaline hydrogen peroxide changes inform in the presence of superoxide, especially when the pH is near orbelow hydrogen peroxide's pKa of 11.6. Likewise, the “free” form ofsuperoxide is quenched by the presence of hydrogen peroxide, especiallyat high concentrations. Hydrogen peroxide has been reported to behave asa stabilizing co-solvent which increases the chemical reactivity ofaqueous superoxide solutions. See “Identification of the Reactive OxygenSpecies Responsible for Carbon Tetrachloride Degradation in ModifiedFenton's Systems,” Watts, et al., Environmental Science & Technology,Vol. 38, No. 20, 2004. Hydrogen peroxide is a weak acid and canpotentially serve as a proton source for superoxide, which has a pKa of4.8. Based on the UV spectra it appears that hydrogen peroxide in itsfully protonated form can interact with superoxide to form a differentspecies, such as, for example, an “adduct,” in an equilibrium processand/or lead to the reactions in Equations 1 and 3. At pH 11, hydrogenperoxide is consumed more rapidly, consistent with the processes inEquations 1 and 3, which produce hydroxyl radicals. A measurableincrease in the concentration of hydrogen peroxide and pH over time wasnever observed indicating that the disproportionation reaction inEquation 6 was negligible for the reactor output.

The stability of the co-generated hydrogen peroxide and superoxideoutput solutions was significantly greater than the lifetimes citedearlier, 1.5 minutes at pH 11 and 41 minutes at pH 12.5 in aqueoussolution. The lifetimes of active species at pH 12 and greater were atleast five hours in the diluted reactor output solutions. The stabilityof the concentrated, undiluted output solutions was lower as evidencedby gas bubble evolution observed after approximately 30 minutes time. AtpH 11 the degradation of active oxygen species was accelerated, butpersisted for at least five hours in the diluted reactor outputsolutions. Enhanced oxidation activity, of these output solutions wasdemonstrated to persist for more than 12 hours at pH 11-12 in theexample cited below.

Example 12 Advanced Oxidation of Methylene Blue with ElectrochemicallyCo-Generated Hydrogen Peroxide and Superoxide

Catholyte output solution was generated by the method cited in Example11 at 5 amps operating current. Output solution contained 2500+/−50 mg/Lhydrogen peroxide and a calculated maximum potential concentration of3050 mg/L superoxide at pH 12.1. 2.0 mL of freshly generated outputsolution was added to 2.0 mL of 100 mg/L methylene blue solutionacidified with bisulfate. The prepared oxidation test solution had aninitial pH of 11.9 and contained 50 mg/L methylene blue, 1250 mg/Lhydrogen peroxide, a maximum potential superoxide concentration of 1500mg/L. Solution temperature was 25° C. The methylene blue color wasevaluated over time by comparison to the series of methylene blue colorstandards as described in Example 9. A slight decrease in colorintensity, ca. 10%, was observed after 5.6 hours had passed without asignificant change in pH. The solution was colorless to the eye after 50hours. For comparison, hydrogen peroxide alone had no visible effect onmethylene blue after several days.

Example 13 Potential Singlet Oxygen Formulation for In-Situ ChemicalOxidation

Singlet oxygen may be used for remediation and decontamination of a bodyof soil, a geologic formation, an excavated soil, and construction ordemolition debris.

The following example is a potential example of singlet oxygenformulation from bulk chemicals, formulated using the system and methodsdepicted in FIGS. 3 and 4, for in-situ chemical oxidation (ISCO) forremediation of soil contaminated with, for example, 60 mg/kg diesel fueland 40 mg/kg polycyclic aromatic hydrocarbons (PAH's). The resultingsinglet oxygen formulation could be used to oxidize 85-95% of thecontaminants, oxygenate the soil and supply non-toxic, low molecularweight organic substrates to heterotrophic bacteria which may consumeresidual contaminants and their oxidation byproducts. The presentexample includes assumptions of a soil porosity of 20%, soil pH 8.0-8.5,soil density is 2.4 g/cm³, soil type is assumed to be clayey with lowvapor permeability, depth of contamination is assumed to be up to 4meters and injection and recovery wells could be used.

Chemical feeds used in, for example, the system 300 of FIG. 3 and method400 of FIG. 4 could include applying six soil pore volumes of oxidantformulation containing a 4:1 mass ratio of peroxyacetic acid tocontaminant to set the singlet oxygen dose, and a treatment rate of 32cubic yards per day. Chemical inputs on a 100% basis may be 24.3 lb/dayhydrogen peroxide, 40.7 lb/day sodium hydroxide, 9.8 lb/day hydrochloricacid, 103.9 lb/day triacetin and 7942 gal/day water. The injectionconcentrations of oxidant formulation constituents may be about 800 mg/Lperoxyacetic acid, <15 mg/L hydrogen peroxide, 664 mg/L glycerol, 912mg/L sodium acetate, 238 mg/L sodium chloride and an initial solution pHof 8.5-9.5. Additional sodium chloride may be added to match thesalinity of the soil if necessary. Non-toxic additives includingco-solvents (e.g., triacetin, glycerol), compatible surfactants (e.g.,sodium dodecyl sulfate) and stabilizers (e.g., phytic acid) may be addedto enhance performance. The prepared formulation may be fed as a liquidinto injection wells to infiltrate the soil at ambient temperature. Aresidence time of at least six hours may be expected to provide singletoxygen generation activity, provide peroxyacetic acid reaction time withcontaminants and also allow Fenton-like peroxide activation processes tooccur with any reduced iron minerals present.

Recovered, spent flushing fluids may have a pH similar to that of thesoil body and contain salinity, hardness (e.g., calcium/magnesiumcarbonate), suspended solids (e.g., iron or manganese oxides), glycerol,acetate, additives, oxidation byproducts (e.g., nitrate, low molecularweight hydrocarbons) and potentially non-oxidized contaminants andmicrobes. The spent flushing fluids may be treated on site fordischarge, sent to a municipal water treatment facility, disposed of inan injection well, or processed for water recovery and recycle back intothe remediation process or other use.

Example 14 Potential Superoxide Formulation for Ex-Situ ChemicalOxidation and Reduction for Remediation

Superoxide formulations may be used for remediation and decontaminationof a body of soil, a geologic formation, an excavated soil, andconstruction or demolition debris.

The following example shows a potential superoxide formulation for exsitu chemical oxidation for remediation of soil contaminated with, forexample, 10 mg/kg non-aqueous phase liquids (NAPL) containing lowvolatility halogenated materials such as brominated flame retardants,dioxins, and polychlorinated biphenyls (PCB's), formulated using thesystem of FIG. 5, for example. The resulting superoxide formulation maybe used to chemically oxidize more than 99% of the contaminants andflush residuals out of the soil. In the present example, it is assumedthat there is a pH 7.0-7.5, average soil density is 2.4 g/cm³, and soiltype is a sand/alluvial mixture. The soil is excavated for treatment andthen returned to its origin.

In the present example, chemical feeds may be assumed to includeapplying the equivalent of 4 soil pore volumes (20% porosity assumed) ofsuperoxide formulation containing a 3:1 mass ratio of hydrogen peroxideto contaminant to set the superoxide dose, and a treatment rate of 32cubic yards per day. Chemical input and output rates are calculatedbased on the process described for FIGS. 7 and 11, using anelectrochemical reactor of type in FIG. 6. Inputs into theelectrochemical generator may be 834 lb/day sodium sulfate, 218 gal/daywater, 5600 L/day oxygen gas at STP and approximately 1070 kWh per dayto operate the system. The reactor may produce 100 lb/day hydrogenperoxide at 40% current efficiency (produced as sodium peroxide), amaximum potential mass of 235 lb/day superoxide at about 50% currentefficiency (produced as sodium superoxide), approximately 28 lb/daysodium hydroxide and, in a separate output stream, 711 lb/day sodiumbisulfate. Sodium bisulfate may be used for pH adjustment of superoxideformulations and treated soil. The reactor output may be diluted with4880 gal/day water to produce an oxidant formulation of about 90 mg/Lhydrogen peroxide, up to 212 mg/L superoxide, up to 750 mg/L sodiumsulfate and an initial solution pH of 10.5-11.5. A relatively lowconcentration of oxidants may be necessary to avoid their quenching ofgenerated hydroxyl radicals, similar to an ultraviolet-hydrogen peroxideadvanced oxidation process. Other additives such as surfactants andco-solvents may be used selectively or not at all to minimizeconsumption of hydroxyl radicals produced by the formulation. Theprepared formulation may then be applied as a liquid to the excavatedsoil and allowed to contact the soil for a period of time at ambienttemperature or elevated temperature. The soil may also be flushed in asecond step with excess co-generated acid, sodium bisulfate not used inthe formulation pH adjustment, to balance the pH of the soil if becomeselevated during treatment.

Recovered, spent soil washing fluids may be expected to have a pHsimilar to that of the soil and contain salinity, hardness (e.g.,calcium/magnesium carbonate), additives and potentially oxidation orreduction byproducts or non-oxidized or reduced contaminants andmicrobes. The spent flushing fluids may be treated on site fordischarge, sent to a hazardous waste facility, disposed of in aninjection well, or processed for water recovery and recycle back intothe remediation process or other use.

Example 15 Clean in Place (CIP) Applications for Food, Beverage, Dairy,and Biopharma Processing Equipment Cleaning

Clean in place (CIP) applications involve the preparation of cleansersand sanitizer solutions and dispensing them into pipes, tanks and otherprocessing equipment that is not disassembled for cleaning. The chemicalactivity of such solutions provides the cleansing and sanitizingcapabilities. CIP cleansers and sanitizers are prepared in day tanks,often ranging in capacity from 50 to 500 gallons, and distributed toequipment when needed during cleaning cycles. Alkaline cleansers andoxidizing alkaline cleansers may be particularly useful for removingsoils and organic residues, acids for removing scaling minerals andantimicrobial sanitizers for disinfection. The use of non-chlorine basedcleansers and sanitizers may minimize corrosion of stainless steelprocessing equipment and to avoid chlorinated oxidation or disinfectionbyproducts.

Acid compatible sanitizers, such as peroxyacetic acid, may reduce thenumber of system cleaning flushes relative to chlorine and chlorinebleach based sanitizers, which are not compatible with acid pH of lessthan about pH 4 due to the release of chlorine gas. Alkaline oxidizingcleansers may be more effective at removing organic soils, proteins andfat deposits than alkali detergents alone. See U.S. Pat. No. 7,754,064,FIGS. 13-14.

FIG. 17 shows an exemplary system and flow process for electrochemicallygenerating a CIP cleanser, in one embodiment. The following exampleshows an electrochemically generated CIP cleanser and sanitizerformulations for use in food, beverage, dairy and biopharma processingequipment. Alkaline oxidizing cleanser 1720 and acid sanitizer 1722 areco-generated and stored in 500 gallon day tanks 1716, 1718, respectivelyuntil use. The alkaline oxidizing cleanser 1720 is formulated to contain0.01 mol/L NaOH (pH 12.0) and 200 mg/L peroxyacetic acid to generatesinglet oxygen, generated by method 500, for example. The acid sanitizer1722 is formulated to contain 0.02 mol/L citric acid (pH 2.6) and 400mg/L peroxyacetic acid, generated by, for example, the electrochemicalreactor of FIG. 6. Surfactants and stabilizers may be used in eithercleanser or sanitizer solution, but are not required, and not shown inFIG. 17. Cleanser solutions 1720, 1722 may be heated to 55-60° C. priorto distribution as is customary for CIP processes.

The above specified formulations use two identical electrochemicalreactors, for example the electrochemical reactor discussed withreference to FIG. 6 above, with the exception of their cathode surfacecompositions and feed rates, in parallel to generate the requiredchemicals by the process outlined in FIG. 17. Electrochemical productionis designed for 500 gallons each of alkaline and acid cleansers. Reactorinputs makeup water 1702, brine 1704, oxygen gas 1706, and power source1708 and outputs 1724, 1726 are listed on a 100% basis.

Electrochemical Reactor 1714 contains an activated carbon cathodesurface for high efficiency hydrogen peroxide production and producesalkaline hydrogen peroxide and citric acid concentrates in two separateoutput streams. Inputs for Reactor 1714 are 6.93 lb/day sodium citrate1704, 230 L/day oxygen gas 1706 at STP, 15 gal/day water 1702(1) andapproximately 9.9 kWh electricity 1708 to operate the system. Outputsfor Reactor 1714 are (i) an alkaline H₂O₂ concentrate 1724 including1.12 lb/day hydrogen peroxide (at 84% cathode current efficiency)combined with 0.38 lb/day sodium hydroxide and (i) an acid concentrateoutput 1726 including 4.53 lb/day citric acid in a separate stream. Thealkaline hydrogen peroxide 1724 is reacted with 4.78 lb/day triacetin1710 and two thirds of the resulting peroxyacetic acid solution 1724′ isfed to the alkaline cleanser holding tank 1716 while the remainder isfed to the acid sanitizer holding tank 1718. Less than about 15 mg/Lhydrogen peroxide is present in the peroxyacetic acid output 1724′.

Electrochemical Reactor 1715 contains a nickel cathode surface for highefficiency sodium hydroxide production and produces alkaline hydrogenperoxide 1728 and citric acid 1730 concentrates in two separate outputstreams. Inputs for Reactor 1715 are 17.7 lb/day sodium citrate 1705,320 L/day oxygen gas 1707 at STP, 17 gal/day water 1702(2) andapproximately 18.3 kWh electricity 1709 to operate the system. Outputsfor Reactor 1715 are 1.66 lb/day sodium hydroxide 1728 (at 98% cathodecurrent efficiency) and 11.57 lb/day citric acid 1730 in a separatestream. The sodium hydroxide 1728 is fed to the alkaline cleanserholding tank 1716 while the citric acid 1730 is fed to the acidsanitizer holding tank 1718.

The alkaline cleanser holding tank 1716 and acid sanitizer holding tanks1718 are filled with water 1702 during chemical production bringingtheir final volumes to 500 gallons each. The use of triacetin 1710 togenerate the peroxyacetic acid 1724′ results in about 340 mg/L glycerolplus 475 mg/L sodium acetate in the alkaline cleanser and 170 mg/Lglycerol plus 235 mg/L acetic acid in the acid sanitizer 1722.

In some exemplary CIP applications milder cleansers are desirable.Singlet oxygen generation is not desirable when certain materials aresusceptible to degradation by singlet oxygen. Relevant examples includedesalination filter membranes and polymers including polyamides,polysulfone, polyurethane, polyetheylene terephthalate, epoxy resins,polyacrylonitrile-butadiene copolymer (nitrile rubber) and naturalrubber. To quench singlet oxygen generation by the alkaline cleansersolution described in the above CIP example a lower amount of triacetin1710 is used thereby leaving a hydrogen peroxide concentration, incombination with peracid solution 1724′, high enough to quench singletoxygen evolved by peroxyacetic acid. For example, the triacetin input1710 may be decreased by 67% to about 1.63 lb/day thereby increasing thehydrogen peroxide concentration to about 100 mg/L and decreasing theperoxyacetic acid concentration to about 200 mg/L in the alkalinecleanser solution 1720. As a result the acid sanitizing solution 1722will contain about 50 mg/L hydrogen peroxide and 100 mg/L peroxyaceticacid. The alkali and acid concentrations remain virtually unchangedunless their production by Electrochemical reactor 1715 is decreased.

Example 16 Singlet Oxygen Production Using Bulk Chemicals for OilProduction Well Flushing Applications

Well casings and pipelines are serviced to remove bacterial growth,slime buildup, mineral scale deposits, corrosion and contamination.These issues are common between oil and gas production wells andpipelines, groundwater wells, raw water and wastewater pipelines andpotable water and greywater distribution systems. Microbial control,removal of slime (the decaying remains of dead bacteria and otherorganic materials), microbial corrosion control and scale removal aresignificant maintenance issues for prolonging the production capacityand lifetime of a well. Pipelines carrying raw water, wastewater,produced water, greywater and other untreated water will encountermicrobial growth and slime formation and will require cleaning. Methodsfor cleaning well bore casings and pipelines include chemical flushingwith oxidizers and acids and mechanical cleaning such as brushing andscraping.

Compatibility of oxidants with seawater and brackish water is desirablein locations where there are no natural freshwater resources available.Flushing solution activity should persist for at least 5 hours and beeffective in the range of pH 8-9. Ideally flushing solutions should bepH balanced and be safe for municipal disposal or discharge.

The following example presents an application of chemical flushing of anoil production well with a singlet oxygen formulation made from bulkchemicals. The singlet oxygen formulation may be created using method400 and system 300 discussed above. In the following example, theproduction well may be located in a coastal region where seawater isused as floodwater for enhanced oil recovery. The well depth may beassumed to be 12,000 feet below surface and may have an average casingdiameter of 6 inches and volume of about 4,630 gallons.

In this example, chemical inputs and outputs are stated as quantitiesper well volume. Chemical inputs on a 100% basis may be 5.4 lb hydrogenperoxide, 8.9 lb sodium hydroxide, 2.2 lb hydrochloric acid, 22.8 lbtriacetin, 9.6 lb nonionic polyether alcohol surfactant/wetting agentand 4630 gal water of which the majority (e.g., >90%) may be seawaterfiltered through a 1 micron rated filter. The prepared injectionconcentrations of oxidant formulation constituents may be about 300 mg/Lperoxyacetic acid, <10 mg/L hydrogen peroxide, 250 mg/L glycerol, 340mg/L sodium acetate, 250 mg/L surfactant/wetting agent, 90 mg/L sodiumchloride (not including the salt added by seawater) and an initial pH of8.5-9.5. An oxidant-compatible corrosion inhibitor such as tetrasodiumpyrophosphate may also be added to enhance performance.

The above prepared formulation may be fed as a liquid into a well bore(or pipeline) at ambient temperature. A residence time of at least fourto six hours may be expected to provide singlet oxygen generationactivity and oxidative breakdown of organic materials; provideperoxyacetic acid contact time with microbes; and allow Fenton-likeperoxide activation processes to occur with catalytically active reducediron surfaces or other metal surfaces present.

The use of seawater, with a natural bromide content of about 65 mg/L, asthe primary water source for the flushing solution may be expected toprovide some hypobromous acid or hypobromite ion by oxidation of bromideby peroxyacetic acid. Hypobromous acid may be an additional oxidant thatcan participate in the performance of the singlet oxygen flushingsolution and has significant oxidation and antimicrobial activity up toabout pH 8.5.

Recovered, spent flushing fluids may be expected to have a pH similar tothat of seawater or groundwater and contain salinity, hardness (e.g.,calcium/magnesium carbonate), suspended solids (e.g., iron or manganeseoxides), suspended organic materials such as slime deposits, glycerol,acetate, surfactant and corrosion inhibitor additives, oxidationbyproducts (e.g., nitrate, low molecular weight hydrocarbons) andpotentially non-oxidized contaminants and microbes. The spent flushingfluids may be treated on site for discharge, sent to a municipal watertreatment facility, disposed of in an injection well, or processed forwater recovery and recycle back into well operations.

Example 17 Potential Superoxide Formulation for Oil Sand Tailing PondWater Treatment

Oil Sand Tailing Ponds in northern Alberta, Canada represent a verylarge impoundment of contaminated and toxic water created by bitumenextraction and processing. Water quality has been degraded throughmultiple reuse cycles to the point that it is no longer suitable forreuse. Natural biodegradation and attenuation of contaminants can beextremely slow or ineffective for remediating these waters due to thepresence of recalcitrant organic contaminants such as naphthenic acids,phenols and polycyclic aromatic hydrocarbons and cold temperatures. Arepresentative composition of tailing pond water for this treatmentexample can include 2000 mg/L inorganic TDS, pH 8.3, 0.025 mg/L cyanide,50 mg/L naphthenic acids, 10 mg/L oil and grease, 0.5 mg/L phenols, 0.01mg/L polycyclic aromatic hydrocarbons, and several trace metals such asiron (2 mg/L), copper (0.05 mg/L), chromium (0.01 mg/L), and lead (0.1mg/L) to name a few.

The general treatment strategy is to oxidize recalcitrant organiccontaminants with a superoxide and hydrogen peroxide formulation toallow for more rapid treatment of smaller organic fragments downstreamin a biological treatment process. Oxidation is primarily provided byhydroxyl radicals formed directly by superoxide and hydrogen peroxide bythe reactions in Equations [4] and [6]. Hydroxyl radicals are alsoexpected to be formed by Fenton chemistry with catalytically activemetals surfaces present in the tailing pond water including iron andcopper. Waste heat from equipment and bitumen processing can provideheat to support treatment operations.

A generation system from FIG. 18 was used in the present example to showan exemplar of producing a superoxide precursor formulation using anelectrochemical generator, in one embodiment. Superoxide concentrate1124 and, optionally, acid concentrate 1126 are electrochemicallygenerated using an electrochemical reactor 1114. Electrochemicalreduction of oxygen is conducted at a suitable cathode and water isoxidized at a suitable anode in an electrochemical reactor 1114 in whichthe anode and cathode chambers are separated by a membrane. Oxygen gas1106 and a 2 g/L aqueous sodium sulfate solution 1104 are supplied tothe cathode while a 47.5 g/L aqueous sodium sulfate solution 1104 issupplied to the anode. A direct current 1108 is applied to theelectrodes thereby driving the reduction of oxygen at the cathode toproduce superoxide, hydrogen peroxide and sodium hydroxide as themajority products 1124 of the cathode, while water is oxidized at theanode to produce sodium bisulfate acid and oxygen gas as the majorityproducts 1126 of the anode.

In this example the cathode product solution 1810 has a composition ofapproximately 8.2 g/L superoxide (as O₂*⁻), 5.0 g/L hydrogen peroxide(as H₂O₂), 1.3 g/L sodium hydroxide and a pH of about 12.6 (as NaOH)assuming a 40% current efficiency for oxygen reduction to superoxide and50% current efficiency for oxygen reduction to hydrogen peroxide. Theanode product solution 1812 has a composition of approximately 30 g/Lsodium bisulfate and 13 g/L sodium sulfate assuming about 90% sodiumsulfate to sodium bisulfate acid conversion. The anode to cathodeproduct solution volume ratio is about 1.73.

The superoxide-containing cathode product solution 1810 is then dilutedto its point of use concentration (i.e., 75 mg/L hydrogen peroxide, 124mg/L superoxide, 20 mg/L NaOH) by mixing directly with raw tailing pondwater 1820 in a 1:65.7 volume ratio. This mixture is held in anoxidation tank 1124 with a residence time of 6 to 24 hours after whichthe oxidized water is pH adjusted with the anode product solution 1126in a 38.5:1 volume ratio. The pH-adjusted oxidized tailing pond water1822 is then sent to a secondary treatment process. An example of asecondary treatment process is an aerobic bioreactor stage, to removeorganic residuals and nitrification, followed by an anaerobic bioreactorstage, for sulfate reduction, removal of metal as sulfides anddenitrification.

1-27. (canceled)
 28. A reactive oxygen species precursor formulationcomprising a peracid concentrate capable of generating singlet oxygen,the peracid concentrate comprising a mixture of an alkaline concentrate,hydrogen peroxide and an acyl donor, wherein the reactive oxygen speciesprecursor formulation has a pH value ranging from about pH 9.5 to aboutpH 12.5 and a peracid anion to peracid molar ratio greater than about1:1.
 29. The reactive oxygen species precursor formulation of claim 28,wherein the molar ratio of hydrogen peroxide to acyl donor reactivegroups is in the range of about 1:1.25 to about 1:4.
 30. The reactiveoxygen species precursor formulation of claim 28, wherein the reactiveoxygen species precursor formulation undergoes the following chemicalreaction:AcOOH+AcOO⁻→¹O₂+AcOH+AcO⁻.
 31. The reactive oxygen species precursorformulation of claim 28, wherein the reactive oxygen species precursorformulation is a singlet oxygen precursor formulation.
 32. The reactiveoxygen species precursor formulation of claim 28, wherein the acyl donoris an acetyl donor.
 33. The reactive oxygen species precursorformulation of claim 28, wherein the acyl donor is one of an oxygen-acylor oxygen-acetyl donor or a nitrogen-acyl or nitrogen-acetyl donor. 34.The reactive oxygen species precursor formulation of claim 28, whereinthe peracid concentrate has minimal hydrogen peroxide residual.
 35. Thereactive oxygen species precursor formulation of claim 28, wherein theperacid concentrate has a minimal hydrogen peroxide residual to minimizequenching of singlet oxygen.
 36. The reactive oxygen species precursorformulation of claim 28, wherein the peracid concentrate has a molarratio of peracetic acid to hydrogen peroxide of at least about 32:1. 37.A method for oxidizing a contaminant, comprising: contacting a reactiveoxygen precursor formulation with an aqueous stream containing thecontaminant, wherein the reactive oxygen precursor formulationcomprises: a peracid anion to peracid molar ratio of 1:1 or more; and apH value ranging from about pH 9.5 to about pH 12.5, wherein thecontacting of the reactive oxygen precursor formulation with the aqueousstream generates a reactive oxygen species and oxidizes the contaminant.38. The method of claim 37, wherein the aqueous stream is one of ahydraulic fracturing water or produced water from a subsurfaceformation.
 39. The method of claim 37, wherein the contaminant is one ormore of an organic material, inorganic materials, metals, suspendedsolids, silt, petrochemical, bacteria, slime, and microbes.
 40. Themethod of claim 37, wherein the reactive oxygen precursor formulation isa singlet oxygen precursor formulation.
 41. The method of claim 37,wherein the reactive oxygen precursor formulation has a minimal hydrogenperoxide residual to minimize quenching of singlet oxygen.
 42. Themethod of claim 37, wherein the reactive oxygen precursor formulationhas a molar ratio of peracetic acid to hydrogen peroxide of at leastabout 32:1.
 43. A method for oxidizing a contaminant, comprising:contacting a reactive oxygen precursor formulation with one of ahydraulic fracturing water, a produced water from a subsurface formationor an oil and/or gas production well water containing the contaminant,wherein the reactive oxygen precursor formulation has: a peracetateanion to peracetic acid molar ratio of 1:1 or more; and a pH valueranging from about pH 9.5 to about pH 12.5, wherein the contacting ofthe reactive oxygen precursor formulation with the one of the hydraulicfracturing water, the produced water from a subsurface formation or theoil and/or gas production well water generates an oxygen species andoxidizes the contaminant.
 44. The method of claim 43, wherein thecontaminant is one or more of an organic material, inorganic materials,metals, suspended solids, silt, petrochemical, bacteria, slime, andmicrobes.
 45. The method of claim 43, wherein the reactive oxygenprecursor formulation is a singlet oxygen precursor formulation.
 46. Themethod of claim 43, wherein the reactive oxygen precursor formulationhas a minimal hydrogen peroxide residual to minimize quenching ofsinglet oxygen.
 47. The method of claim 43, wherein the reactive oxygenprecursor formulation has a molar ratio of peracetic acid to hydrogenperoxide of at least about 32:1.